An image forming apparatus includes a rotary developing device having a developing device main body rotatably disposed and a plurality of developing units arranged along a rotation direction of the developing device main body, a frame for supporting the rotary developing device in free rotation, and a drive source for rotationally driving the rotary developing device, characterized in that the drive source for rotationally driving the rotary developing device is disposed in an area to which the rotary developing device is projected in a direction orthogonal to a rotation axis.