a housing;

an endless belt that is mounted in the housing and that conveys either one of a developer image and a recording medium;

a plurality of process units that are mounted in the housing in one to one correspondence with a plurality of colors, the plurality of process units including a plurality of photosensitive drums, respectively, each photosensitive drum facing the endless belt;

a plurality of scanner units that are mounted in the housing and that are provided one for each of the photosensitive drums, each scanner unit scanning with light the surface of the corresponding photosensitive drum to form an electrostatic latent image, each process unit developing the electrostatic latent image by using a developer of the corresponding color; and

a transfer portion that is mounted in the housing and that transfers the developer image, formed on the surface of each of the photosensitive drums, onto either one of the endless belt and the recording medium that is conveyed by the endless belt,

the scanner units and the process units being disposed alternately in a horizontal direction,

each scanner unit and each process unit being inclined obliquely to a vertical direction,

at least a part of each process unit being inserted into and removed from the housing in an obliquely inclined direction, wherein each scanner unit includes:

a scanner housing;

a light source mounted in the scanner housing; and

a deflecting unit that is mounted in the scanner housing and that deflects a light beam emitted from the light source to scan the surface of the corresponding photosensitive drum; and

further comprising:

a plurality of support frames, each of which is fixedly mounted in the housing and supports thereon the corresponding scanner housing;

a regulation unit that regulates at least a part of the scanner housing to be away from the support frame; and

an adjustment unit that adjusts the orientation of the scanner housing relative to the support frame

the scanner housing has a scanner surface positioned facing the support frame;

the support frame has a frame surface that is positioned facing the scanner surface;

the regulation unit includes:

a rotational shaft provided in the scanner housing to extend in a direction along the scanner surface; and

a bearing portion protruding from the frame surface in a direction defined to extend from the frame surface toward the scanner surface, the bearing portion rotatably receiving the rotational shaft; and

the adjustment unit causes the scanner housing to pivot about a contact portion between the rotational shaft and the bearing portion to adjust the orientation of the scanner housing relative to the support frame, the rotational shaft is located at substantially a central portion in a scanning path, in which the deflecting unit scans the light beam, and extends orthogonal to the scan direction;

the scanner surface has a first end portion and a second end portion in a scanning direction in which the deflecting unit scans the light beam along the scanning path; and

the adjustment unit includes:

a leaf spring provided on one side of the scanner surface that is nearer to the first end portion than to the second end portion and urging the first end portion towards the frame surface; and

a screw provided on the other side of the scanner surface that is nearer to the second end portion than to the first end portion and adjusting a distance between the second end portion of the scanner surface and the frame surface against the urging force of the leaf spring.