A motor driving device according to the present invention includes: a PWM duty ratio detecting unit for detecting a target rotational speed based on a duty ratio of a PWM signal input from a host system; a PWM period detecting unit for detecting a period of the PWM signal; a PWM period error calculating unit for calculating an error between a PWM period output from the PWM period detecting unit and a PWM period previously set as a reference calculated by using the operational clock generator; a position detecting sensor for detecting a permanent magnet of the rotor; and an actual rotational speed calculating unit for calculating an actual rotational speed of the rotor by using a signal output from the position detecting sensor. The present motor driving device controls a speed while correcting the actual rotational speed based on the PWM period error.