An image forming apparatus has a high-speed mode and a low-speed mode and includes a speed switch unit configured to select the high-speed mode or the low-speed mode by switching a rotation direction of a drive source. The speed switch unit includes a drive gear attached to a rotating shaft of the drive source; a first drive gear series transmitting a rotating power of the drive source upon rotation in a first direction to an image carrier; and a second drive gear series transmitting a rotating power of the drive source upon rotation in a second direction to the image carrier, the second drive gear series having a larger reduction ratio than the first drive gear series. The speed switch unit causes the drive gear to be selectively connected to the first drive gear series or the second drive gear series depending on the rotating direction of the drive source.