Abstract: To provide an improvement capable of simplifying an operation for installing an additionally installable apparatus. An image forming apparatus comprises a apparatus main body 11 and at least one additionally installable apparatus, in which one additionally installable apparatus is detachably disposed to a main body side device composed at least of the apparatus main body 11. The additionally installable apparatus has a positioning member at a surface facing to the main body side device. The main body side device has a receiving portion configured to receive the positioning member at a surface facing to the additionally installable apparatus and a guiding member 22 for guiding the positioning member to the receiving portion.

Abstract: To improve image quality upon preventing abrasion traces from strongly forming on a surface of a fusing member, an invented fusing device has a pressure member, a fusing member movably arranged as faced with the pressure member, and a contact element arranged in contact with an outer circumferential surface of the fusing member, with the surface roughness of the fusing member of 1.0 to 4.0 [?m]. When the fusing member is moved in contact with the contact element, the contact element rubs a surface of the fusing member, but in the fusing member, the portion in contact with the contact element and the portion not in contact with the contact element become about equal in the surface roughness with the above surface roughness.

Abstract: To provide an improvement capable of simplifying an operation for installing an additionally installable apparatus. An image forming apparatus comprises a apparatus main body 11 and at least one additionally installable apparatus, in which one additionally installable apparatus is detachably disposed to a main body side device composed at least of the apparatus main body 11. The additionally installable apparatus has a positioning member at a surface facing to the main body side device. The main body side device has a receiving portion configured to receive the positioning member at a surface facing to the additionally installable apparatus and a guiding member 22 for guiding the positioning member to the receiving portion.

Abstract: To improve image quality upon preventing abrasion traces from strongly forming on a surface of a fusing member, an invented fusing device has a pressure member, a fusing member movably arranged as faced with the pressure member, and a contact element arranged in contact with an outer circumferential surface of the fusing member, with the surface roughness of the fusing member of 1.0 to 4.0 [?m]. When the fusing member is moved in contact with the contact element, the contact element rubs a surface of the fusing member, but in the fusing member, the portion in contact with the contact element and the portion not in contact with the contact element become about equal in the surface roughness with the above surface roughness.