PURPOSE: To smooth the selective switching action of a developing device by bringing an abutting roller into contact with a guiding roller on a developing device side and separating the developing device from an image carrier at the time of rotating a developing device holding body.

CONSTITUTION: A stop arm 65 and a play gear 72 attached to a main frame escape in directions shown by arrows B and C respectively, and the developing device holding body 46 which holds the developing device 4a starts to rotate a direction shown by an arrow A centering around a shaft 45. With the rotation of the holding body 46, the guiding roller 54 comes in contact with the abutting roller 50 and the developing device 4a is turned and displaced centering around a shaft 42 by resisting the energizing force of a spring to be in a recessed state. At such a time, the roller member 58 of a holding means 55 meshes in the space between the roller contact surfaces of latch members 56 and 57 and the recessed state of the developing device 4a is held. The protruding action of the developing device is performed by moving the arm 65 by means of a photosensitive drum 2 and engaging it in a positioning groove 67. Thus, the selective switching action of the developing device is smoothed.