The present invention provides a drive device and drive method of a brushless motor in which it is possible to suppress a decrease in rotational accuracy and controllability by pulse shift control. The drive device detects an open phase voltage during an energization period by pulse width modulation control, estimates position information of a rotor from the detected voltage value, and drives a three-phase brushless motor. When the voltage pulse width of a set duty ratio is equal to or less than a prescribed value, the drive device performs energization of a voltage pulse width of the minimumduty ratio twice during one cycle of pulse width modulation, performs energization of a voltage pulse width of a correction duty ratio twice during one cycle of the next pulse width modulation, and performs energization of a pulse width of a drive duty ratio corresponding to the set duty ratio in an average of two cycles.