An image forming apparatus includes a control unit which controls a correcting operation of correcting the meandering of an endless belt by a roller position adjusting mechanism. Prior to the correcting operation, the control unit causes a toner image for monitoring to be transferred to an area of a circumferential surface of the belt passing a detection area of a density sensor, causes the density sensor to perform a first detecting operation of detecting the toner image for monitoring, subsequently causes the density sensor to perform a second detecting operation of detecting the toner image for monitoring after the circumferential surface of the belt is moved by a predetermined distance, and calculates a meandering amount of the belt by comparing a first density value obtained by the first detecting operation and a second density value obtained by the second detecting operation.