A color electrophotographic image forming apparatus detachably mounts cartridges and includes a support supporting a cartridge, movable between inside and outside positions, an outer wall having an opening through which the support passes through when moving between the inside and outside positions, and a guide supporting the support to linearly move between the inside and outside positions so that when the support is in the outside position, the guide supports the support so that a downstream side thereof is pivotable downwardly about an upstream side of the support with respect to a movement direction to the outside position from the inside position. In this state, the cartridge is mounted to the support from above the support and is dismounted upwardly of the support.