To provide a motor drive unit which is reduced in the number of part items and can be manufactured at low cost.

Short circuiting of a circuit or the lock of a motor is detected, by comparing a voltage difference between a motor-side voltage Vm in a motor-side passage M for connecting a power supply 1 and the motor 2, which is detected by a motor-side voltage monitor circuit 8 and a control-side voltage Vc in a control-side passage C for connecting the power supply 1 and an integrated circuit (IC)4, which is detected by a control-side voltage monitor circuit 9 with a prescribed threshold by using the integrated circuit (IC)4.