An image forming apparatus includes a plurality of image carriers, a drive mechanism, a plurality of drive force transmission gears, a phase difference detector, and a shift unit. The plurality of image carriers forms images of separate colors. The drive mechanism including a single drive unit for driving the plurality of image carriers simultaneously. The plurality of drive force transmission gears, provided for each of the image carriers, transmits a driving force from the drive unit to the image carriers. The phase difference detector detects a phase difference in drive speed among the image carriers. The shift unit, provided for each of the plurality of drive force transmission gears, meshes or unmeshes the drive force transmission gear to the drive mechanism. The shift unit is activated to correct any phase difference in drive speed of the image carriers based on a detection result detected with the phase difference detector.