A motor drive device comprising an H-bridge circuit having four switching elements connected in an H bridge form to a motor coil L, a control circuit for on-off controlling each switching element, and a PWM signal generating circuit for generating a PWM signal having a duty according to a ration between a power supply voltage Vcc and a control voltage Vref, wherein the control circuit is so constituted as to select a switching element to be turned on according to an operation mode control signal FIN, RIN and control its on-duty according to the PWM signal. This constitution can variably control easily and over a wide range a drive voltage applied to one end of the motor coil L according to an externally input control voltage Vref.