A laser printer is detachably provided with a carrier belt, support rollers for supporting the carrier belt, and a belt unit provided with a belt frame. A unit support portion for supporting a bearing portion of the support roller and a unit support portion for supporting a bearing portion of the support roller are provided at a side of the main body of the apparatus. Urging by a coil spring allows the bearing portion to press the unit support portion against the support roller. An image forming unit that contains four process cartridges is detachably provided above the belt unit opposite to the belt. The belt unit may be removed from the main body by detaching the image forming unit.