An image forming apparatus forms an image on a recording medium using first to fourth toners, and includes an intermediate transfer target; a primary transfer unit that transfers a first toner image, a second toner image, a third toner image, and a fourth toner image to the intermediate transfer target in stated order; and a secondary transfer unit that collectively transfers the first to fourth toner images onto the recording medium. The first toner image, the second toner image, the third toner image, and the fourth toner image include the first toner, the second toner, the third toner, and the fourth toner, respectively. The first to fourth toners each include toner particles. The toner particles each include a toner mother particle and an external additive attached to the surface of the toner mother particle. The external additive includes fluororesin particles and silica particles.

An imaging system includes a transfer belt that is rotatable, a transfer roller that contacts the transfer belt, and a conductive device that contacts a surface of the transfer roller, to supply a bias to the transfer roller. The transfer roller has a hollow portion.

An intermediary transfer belt having surface resistivity ρs of 1×10.sup.9 Ω/square or more and volume resistivity ρv of 1×10.sup.12 Ω.Math.cm or less includes a thermoplastic resin material containing carbon black. The carbon black contained in the thermoplastic resin material has a weight ratio of 22.5-28.5 weight % and include first carbon black and second carbon black. The first carbon black of the carbon black contained in the thermoplastic resin material has a weight ratio of 50-90 weight % and dibutyl phthalate absorption of 93-127 ml/100 g, and the second carbon black of the carbon black contained in the thermoplastic resin material has a weight ratio of 10-50 weight % and dibutyl phthalate absorption of 36-79 ml/100 g.

An electroconductive elastic body includes: a cross-linked product of a first ionic electro-conductive rubber, a cross-linked product of a second ionic electro-conductive rubber, and at least one of a fatty acid and a fatty acid metal salt; wherein the electroconductive elastic body has a matrix that includes the cross-linked product of the first ionic electro-conductive rubber, and a domain that includes the cross-linked product of the second ionic electro-conductive rubber; the cross-linked product of the second ionic electro-conductive rubber includes a polyether skeleton; an electrical resistance of the domain is lower than an electrical resistance of the matrix; in a waveform separation profile of the elastic body as obtained by a small-angle X-ray scattering method, A2 and A1 satisfy a relationship expressed by the following expression (1):
0.005≤(A2×C2/A1×C1)≤0.030  (1).

An image forming apparatus includes: a transfer cylinder that is supported on an image forming apparatus body and rotates; a rotating member that is coaxial with the transfer cylinder and rotates integrally with the transfer cylinder; a circulating member that is provided with a holding part that holds a front end portion of a recording medium, is suspended around the rotating member, and transports the recording medium by circulating as the rotating member rotates; a transfer unit that is supported on the image forming apparatus body and has a transfer belt that transfers an image on a recording medium transported by the circulating member by sandwiching the recording medium together with the transfer cylinder at a nip position; a first image forming part that is supported on the image forming apparatus body and forms the image on the transfer belt; and a second image forming part that is supported on the image forming apparatus body at a position lower than the first image forming part and forms the image on the transfer belt. Mass of the second image forming part is larger than mass of the first image forming part.

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.

A transfer device includes a plurality of photoconductors, a belt, a plurality of primary transfer rollers and control circuitry. The plurality of primary transfer rollers is disposed for the plurality of photoconductors, respectively. The plurality of primary transfer rollers brings the belt into contact with or separate the belt from the plurality of photoconductors. The control circuitry causes at least one of the plurality of primary transfer rollers to press against a corresponding at least one of the plurality of photoconductors to shift a printing mode.

A transfer unit includes first and second rollers, first and second bearing members, a roller holder, first and second urging members, a switching cam, and a driving mechanism. The switching cam includes first and second guide holes with which first and second engaging portions formed on the first and second bearing members engage. The first and second guide holes are formed, each in an approximately arcuate shape, at positions at different distances from the rotation center of the switching cam. By rotating the roller holder, one of the first and second rollers is arranged opposite an image carrying member and, by rotating the switching cam, the first or second roller arranged opposite the image carrying member is arranged selectively either at a reference position where the first or second roller is in pressed contact with the image carrying member or at a released position.

An image forming apparatus includes: an image carrier body to be transported; an image forming unit that forms an image on the image carrier body; a change roller that is in contact with an inner peripheral surface of the image carrier body so as to be rotatable around a rotation axis and that is capable of changing an angle of the rotation axis with respect to a width direction of the image carrier body; a flywheel provided at the change roller; and a driving mechanism that applies a driving force for changing an angle of the rotation axis with respect to the width direction to an applied portion that moves together with the change roller. A direction of the driving force applied to the applied portion by the driving mechanism is opposite to a direction in which the applied portion moves due to gravity acting on the flywheel.

A pressure device applies pressure to a sheet medium on part of a surface of which an image bearer is formed. The pressure device includes: a driving unit that changes a distance between a first pressing unit and a second pressing unit; a control unit that controls the driving unit such that the distance between the first pressing unit and the second pressing unit becomes a set target value; and a target setting unit that sets the target value to a first distance that is larger than a thickness of the sheet medium when the sheet medium is not present between the first pressing unit and the second pressing unit, and sets the target value to a second distance for applying a target pressure to the sheet medium when the sheet medium and the image bearer are present between the first pressing unit and the second pressing unit.