An image forming apparatus includes image bearing members, an intermediate transfer member, a transfer unit, a control unit, and image forming units respectively corresponding to the image bearing members and each configured to form and transfer an image to the intermediate transfer member, which is then transferred to the conveyed recording material. Image patterns on the intermediate transfer member are detected for positional deviation detection. In a first mode, timing of image formation is determined using a first reference. In a second mode, timing of image formation is determined using a second reference. Based on timings at which formed image patterns are detected, the control unit, in the second mode, corrects timing of image formation performed by a second image forming unit or corrects timing at which the recording material is conveyed to the transfer unit.