Image forming apparatus and method for controlling the same

An image forming apparatus includes an intermediate transfer belt, a driving roller for revolving the intermediate transfer belt, a belt conveyer unit including at least one driving motor for driving the driving roller, an encoder, and a system controller. The encoder detects the rotation speed of the driving roller. The system controller detects a value of the integral of a temporary change in the detected rotation speed and changes, on the basis of the detected integral value, the rotation speed of the driving roller by the integral value in a direction opposite to the temporary change immediately after the temporary change occurs or immediately after the temporary change ends.