An image forming apparatus having a rotation body which is used for transferring an image, a drive section which rotates the rotation body, and a control section which sends a control signal to the drive section to control a speed of the rotation body, the image forming apparatus including: a test signal generating section which generates a test signal and adds it to the control signal; an angular velocity detecting section which detects an angular velocity of the rotation body; and a transfer function calculating section which obtains a latest transfer function of a rotation system including the rotation body and drive section, based on the angular velocity detected by the angular velocity detecting section and the test signal generated by the test signal generating section, wherein the control section controls the drive section, based on the latest transfer function obtained by the transfer function calculating section.