PURPOSE: To obtain a desired control accuracy at a reduced sampling time interval by placing a low-pass filter between a speed detector and a comparator.

CONSTITUTION: The speed control device is provided with a speed detection means 10 for detecting the speed of a direct current motor 8; a comparator 4 for comparing the speed detection signal from the speed detection means 10 and a speed command value; and an automatic speed adjuster 3 which generates the output signal of the comparator 4. In addition a low-pass filter 11 is placed between the speed detector 10 and the comparator 4. In this case a function is provided to calculate a mean value of a specified number of speed detection signals to detect the low-pass filter 11 at a specified time interval and take the resultant mean value as a speed command value. This maintains an appropriate time interval of sampling output to the speed control device and controls the speed of the direct current motor 8 with a desired accuracy.