an image forming apparatus includes a main body , an image carrier provided in the main body and configured to retain electrostatic latent images on its surface , and a developing unit including a holding unit holding plural developing devices , rotatably supported by the main body . further , a driving source is configured to rotate the developing unit and move a desired developing device to a developing position opposed to the image carrier . a stopping member is configured to be moved to an unstopping position unengaged with the holding unit and to a stopping position to stop a one - way direction rotation of the developing unit at an exchanging position for exchanging the developing devices . a backstop member is configured to be moved to a removing position unengaged with the holding unit and to an engaged position engaged with the holding unit to prevent a rotation of the developing unit in a direction opposite the one - way direction rotation .