PURPOSE: To lighten the load of a processor and to facilitate programming by constituting a step motor drive of hardware comprising a shift register, a driver circuit and a clock generator.

CONSTITUTION: A flip-flop 7 is set by a signal ST37 while at the same time a predetermined number is preset in a counter 6 and clock pulses are generated from a clock generator 5 thus shifting shift registers 1, 2 cyclically. The clock pulses are then down counted in the counter 6 and when the count of the counter 6 reaches zero, a carrier pulse is outputted and the flip-flop 7 is reset thus blocking the output from the clock generator 5. A number of pulses preset in the counter 6 is fed, at a time, to a step motor 4. Alternately, logic of a signal MBSY 36 is set at '1' and clock pulses are generated continuously from the clock generator 5. In such a manner, control signals for a driver circuit 3 are obtained from the shift registers 1, 2.