the polarity of the phase difference reversed in accordance with a rotation direction judging signal provided by the cpu 17 and the divided pulse signal provided by divider 19 and outputs these two phase pulse trains to the position controller 5 the counter 6 in the position controller 5 counts the two phase pulse trains and provides a signal representing the number of pulses in the pulse trains to the position control section 7 as in the prior art the number of pulses corresponds to the position of the motor 2 the position control unit 7 then outputs the velocity command signal to the drive control apparatus 22 in accordance with the position command signal generated by the position command generating device 26 and the signal provided by the counter 6 representing the position of the motor 2 the cpu 17 generates a control signal in accordance with the velocity command signal and provides this control signal to the inverter 9 the inverter 9 pulse width modulates the power provided by the three phase alternating current power supply 10 in accordance with the control signal provided by the cpu 17 and thus controls the drive voltage being provided to the motor 2 by the power supply 10 accordingly the above drive control apparatus 22 is compatible with a serial data type position detector 12 and a position controller.