PURPOSE: To prevent fault and malfunction caused by a noise by providing a motor driver circuit inputting a motor driving pattern from an external equipment and outputting an exciting current and a protective circuit prohibiting an electric current supply to a motor when the external equipment for generating a motor drive pattern is unconnected.

CONSTITUTION: A power supply device 1 inputs an electric power from a commercial power source 2 and outputs a motor power 3 and a logic power 10. A motor driver circuit 4 receives the motor power 3 and a motor drive pattern 11, generates a motor exciting current 5, and outputs it to a plurality of motors 6. An electric current path for a motive power to the motors 6 is not passed through a control unit 8, and the motor drive pattern 11 is a logic output without the possibility of a large current flow. Thus, even if a noise occurs, the amount and level thereof is small. When a power is thrown into the motor drive circuit 4 with a connector 25 unconnected to a connector cable from a CPU 9, exciting inputs 32-35 become 'H' through pull-up resistances 26-29 in circuits 7-a, 7-b forming a protective circuit 7 to prevent last-stage drivers 37-40 from being turned ON.