The present invention includes a phase angle detection unit generating a phase angle signal switched at a timing at which a cogging torque generated with the rotation of a rotor of a brushless DC motor reaches near a peak on a negative side hindering the rotation of the rotor, an inverter circuit energizing coils of respective phases of the brushless DC motor by switching elements according to an input of a driving signal, an energization period calculation unit calculating an energization period Tw from a target rotation speed set for the brushless DC motor, and a drive control unit energizing the coils sequentially by outputting the driving signal to the respective switching elements for each energization period, gradually increasing a duty of the driving signals to the switching elements at a start of each energization period, and decreasing the duty after the phase angle signal is switched.