in contact with the slanted surface 119 b of the rotation controlling member 119 thus the pressing of the surface 120 c of the unlocking member 120 by a user causes the rotation controlling member 119 to be moved in the direction indicated by the arrow mark u2212 x against the resiliency of the second spring 118 that is the pressing of the surface 120 c by a user in the direction y in fig4 b causes the rotation controlling member 119 controlling surface 119 c to separate from the cartridge guide 116 first controlling surface 116 b by being guided by the slanted surface 119 b of the rotation controlling member 119 that is the image forming apparatus main assembly a is structured so that as the cover 115 is opened it becomes possible for a user to press the surface 120 c of the unlocking member 120 the unlocking member 120 surface 120 c and rotation controlling member 119 controlling surface 119 b function as a means for switching the position of the cartridge guide 116 from the first position to the second position next the operation in this embodiment for replacing the cartridge in the image forming apparatus main assembly a is described fig1 a shows the position of the cartridge guide 116 during an image forming operation if it is necessary for a user to replace the cartridge in the image forming apparatus main assembly a the user is to open the cover 115 and press the.