A reading module has a light source, an optical system imaging, as image light, reflected light of the light radiated from the light source to the document, and a sensor converting the image light imaged by the optical system into an electrical signal. The optical system has a mirror array in which reflection mirrors are coupled together in an array in the main scanning direction and an aperture stop portion having a first aperture adjusting the amount of image light reflected from a reflection mirror and a second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror. The second aperture is arranged at such a position as to be able to shield stray light passing through a boundary between the reflection mirrors and the center of the first aperture when the mirror array contracts to the maximum extent in the main scanning direction.

Provided is an image forming apparatus capable of accurately returning a carriage to a home position without having to turn ON a light source in the process of returning the carriage to the home position. A first reading-position-detection plate is arranged inside of a reading width of a line sensor and outside of a document-image-reading width. A second color region has a length that gradually increases in the main scanning direction as going away from the home position of the carriage. A reading-position-detecting unit detects the length in the main scanning direction of the second color region on the basis of output from the line sensor. A movement-distance-converting unit converts this length to a movement distance to the home position. A movement-control unit causes the carriage to move toward the home position just the movement distance.

An image reading device includes a housing, a carriage, and a lock mechanism. The housing includes an exterior member and a document sheet placement surface. The carriage is configured to move in the housing along a predetermined specific direction. The lock mechanism is configured to lock the carriage to a lock position. The lock mechanism includes a supported portion and a locking portion. The supported portion is supported by the housing and provided between the exterior member and the carriage disposed at the lock position. The locking portion moves between a first position and a second position in response to a magnetic force of a magnet disposed at a specific position on the exterior member so as to, at the first position, engage the supported portion with the carriage disposed at the lock position, and at the second position, release engagement between the supported portion and the carriage.

A reading module has a light source, an optical system imaging, as image light, reflected light of light radiated from the light source to a document, a sensor where a plurality of imaging regions for converting the image light imaged by the optical system into an electrical signal are arranged next to each other in the main scanning direction, and a housing the light source, the optical system, and the sensor. The optical system has a mirror array where a plurality of reflection mirrors whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction, and an aperture stop portion adjusting the amount of the image light reflected from the reflection mirror. The amount of the image light striking the reflection mirror is increasingly small from opposite end parts of the reflection mirror toward its central part in the main scanning direction.

A reading module has a light source, an optical system imaging, as image light, reflected light of the light radiated from the light source to the document, and a sensor converting the image light imaged by the optical system into an electrical signal. The optical system has a mirror array in which reflection mirrors are coupled together in an array in the main scanning direction and an aperture stop portion having a first aperture adjusting the amount of image light reflected from a reflection mirror and a second aperture shielding stray light that enters the first aperture from an adjacent reflection mirror. The second aperture is arranged at such a position as to be able to shield stray light passing through a boundary between the reflection mirrors and the center of the first aperture when the mirror array contracts to the maximum extent in the main scanning direction.