A transfer unit includes first and second rollers, a roller switching mechanism, and upstream-side and downstream-side guides. The second roller is arranged downstream of the first roller in the conveyance direction of the recording medium. The roller switching mechanism selectively arranges the first or second roller at a reference position to form a transfer nip. The upstream-side and downstream-side guides are respectively arranged upstream and downstream of the transfer nip in the conveyance direction of the recording member. When the first roller moves to the reference position by the roller switching mechanism, the second roller moves to a first retracted position behind the downstream-side guide, and when the second roller moves to the reference position by the roller switching mechanism, the first roller moves to a second retracted position behind the upstream-side guide.

An image forming apparatus includes a formation target that is wound around rotating bodies including a driving roller and transported by the rotating bodies including the driving roller while forming a shape having linear portions each of which forms a different angle, which is an acute angle or an angle of zero degrees, with a horizontal direction when viewed in an axial direction of the driving roller, first image forming bodies that are arranged along one of the linear portions in such a manner as to be spaced apart from each other by a first distance and that form images onto the formation target, and second image forming bodies that are arranged along another one of the linear portions, the other linear portion forming the angle larger than the angle formed by the one linear portion, in such a manner as to be spaced apart from each other by a second distance shorter than the first distance and that form images onto the formation target.

An image forming apparatus includes an image bearing member, a developing member, a controller configured to carry out switching control between a first state in which the developing member is caused to act on the image bearing member and a second state in which the developing member is not caused to act on the image bearing member, a transfer member, and a detector configured to read density information of the recording material. The controller detects a fog density on the basis of a difference in density information between a fog non-occurrence region of a non-image region of the recording material in the second state and a fog occurable region of the non-image region of the recording material in the first state.

An image forming apparatus includes an image bearing member, a developing member, a controller configured to carry out switching control between a first state in which the developing member is caused to act on the image bearing member and a second state in which the developing member is not caused to act on the image bearing member, a transfer member, and a detector configured to read density information of the recording material. The controller detects a fog density on the basis of a difference in density information between a fog non-occurrence region of a non-image region of the recording material in the second state and a fog occurable region of the non-image region of the recording material in the first state.

An image forming apparatus includes an image bearing member, a developing member, a controller configured to carry out switching control between a first state in which the developing member is caused to act on the image bearing member and a second state in which the developing member is not caused to act on the image bearing member, a transfer member, and a detector configured to read density information of the recording material. The controller detects a fog density on the basis of a difference in density information between a fog non-occurrence region of a non-image region of the recording material in the second state and a fog occurable region of the non-image region of the recording material in the first state.

An image forming apparatus includes a formation target that is wound around rotating bodies including a driving roller and transported by the rotating bodies including the driving roller while forming a shape having linear portions each of which forms a different angle, which is an acute angle or an angle of zero degrees, with a horizontal direction when viewed in an axial direction of the driving roller, first image forming bodies that are arranged along one of the linear portions in such a manner as to be spaced apart from each other by a first distance and that form images onto the formation target, and second image forming bodies that are arranged along another one of the linear portions, the other linear portion forming the angle larger than the angle formed by the one linear portion, in such a manner as to be spaced apart from each other by a second distance shorter than the first distance and that form images onto the formation target.

An image forming apparatus includes an image bearing member, a developing member, a controller configured to carry out switching control between a first state in which the developing member is caused to act on the image bearing member and a second state in which the developing member is not caused to act on the image bearing member, a transfer member, and a detector configured to read density information of the recording material. The controller detects a fog density on the basis of a difference intensity information between a fog non-occurrence region of a non-image region of the recording material in the second state and a fog occurable region of the non-image region of the recording material in the first state.

An image forming apparatus that forms an image on a sheet medium under an operation condition set in accordance with a type of the medium, includes a hardware processor that: detects which of a plurality of assumed types the type of the medium applies to, based on output from a sensor; and performs control under which, before the type of the medium is detected, shift to a quasi-rise state, in which preparation for image formation under a provisional condition has partially been completed, is performed, the provisional condition corresponding to an operation condition corresponding to one of the plurality of assumed types, and after the type of the medium is detected, shift to a rise state, in which preparation for image formation under a fixed condition has been completed, is performed, the fixed condition corresponding to an operation condition corresponding to the detected type.

A transfer unit includes first and second rollers, a roller switching mechanism, and upstream-side and downstream-side guides. The second roller is arranged downstream of the first roller in the conveyance direction of the recording medium. The roller switching mechanism selectively arranges the first or second roller at a reference position to form a transfer nip. The upstream-side and downstream-side guides are respectively arranged upstream and downstream of the transfer nip in the conveyance direction of the recording member. When the first roller moves to the reference position by the roller switching mechanism, the second roller moves to a first retracted position behind the downstream-side guide, and when the second roller moves to the reference position by the roller switching mechanism, the first roller moves to a second retracted position behind the upstream-side guide.

An image forming apparatus that forms an image on a sheet medium under an operation condition set in accordance with a type of the medium, includes a hardware processor that: detects which of a plurality of assumed types the type of the medium applies to, based on output from a sensor; and performs control under which, before the type of the medium is detected, shift to a quasi-rise state, in which preparation for image formation under a provisional condition has partially been completed, is performed, the provisional condition corresponding to an operation condition corresponding to one of the plurality of assumed types, and after the type of the medium is detected, shift to a rise state, in which preparation for image formation under a fixed condition has been completed, is performed, the fixed condition corresponding to an operation condition corresponding to the detected type.