Disclosed herein is an image forming apparatus and a control method thereof. According to the control method of the image forming apparatus, entry and exit of a recording medium can be sensed without a register sensor by sensing current change of a press roller used to apply a constant pressure to the recording medium and a transfer belt so as to allow the recording medium and transfer belt to come into close contact with each other. In the case of a model provided with a register sensor, the presence of malfunction of the register sensor can be recognized.