Dc motor driving device

In a DC motor driving device using an open loop control method, whether or not a supplied speed command data corresponds to a drive-instruction is determined according to the speed command data. When it is determined as a drive- instruction, switch means is controlled with a PWM pulse having a predetermined duty ratio in a predetermined acceleration period, to accelerate the DC motor, when the acceleration period is finished, the DC motor is driven by controlling the switch means with a PWM pulse having a duty ratio corresponding to the speed command data. Thereby the endurance current of the switching transistor can be reduced by limiting the starting current at the starting of the device, and the range of controlling the speed of the motor can be broadened by accurately performing the starting.