PURPOSE: To interrupt all the PWM signals easily in an emergency by collectively connecting the cathodes of plural diodes whose anodes are connected to plural PWM output signal lines to pull-up resistors and a collector of a transistor.

CONSTITUTION: When a control power source is turned ON, base current flows to a transistor Tr 5 through a resistance 15 to turn ON the Tr 5. Collector current flows to the Tr 5 through resistances 11 to 14 and anodes 1 to 4. PWM signals A to D are at about 0.7V of diode forward voltage only and motor drive circuits 40 to 43 are turned OFF. Then, in a stable state, when a terminal E is on a level H, a Tr 6 is turned ON and the Tr 5 OFF. To the PWM output terminals A to D the outputs of comparators 7 to 10 are applied as it is. When the terminal E becomes a level L due to a certain abnormality, the Tr 6 is turned OFF and the Tr 5 ON and the signals of comparators 7 to 10 are no longer outputted. In this way, the PWM signal output circuit is easily put to fail-safe and the steering is stopped.