An image forming apparatus includes a plurality of image forming stations and a transferring device. Said cutting tool comprises a rotating cutting body comprising at least one opening forming a cutting edge and through which the liquid flows, the lateral surface of the cutting body facing the rotationally fixed opposite surface that also comprises at least one opening through which the liquid flows. Each of the one or more junctions in one of the levels is directly connected to a respective one of the bit lines. The MPU carries out fault diagnosis of the DC motor, based upon the detected waveform of current when the voltage having the predetermined waveform is applied to the DC motor.