A color image forming apparatus to which cartridges are detachably mountable includes a cartridge supporting member movable between a set position and an outside position; a driving source; a driving member provided opposite to the driving source through the cartridge supporting member, a first driving force transmission member for transmitting a driving force of the driving source; a second driving force transmission member provided oppositely to the first driving force transmission member through the cartridge supporting member; and a third driving force transmission member provided to the cartridge supporting member. The third driving force transmission member is, in a state in which the cartridge supporting member is located at the set position, connected to the first and second driving force transmission members to transmit the driving force of the driving source to the driving member.