To provide a motor without a sensor which can reduce a power consumption and which can be started certainly.

A drive device of the motor without sensor includes a plurality of source transistors and a plurality of sink transistors for energizing selectively the two phase coils of three phase coils, a pulse circuit for turning on and off one of the source transistors and the sink transistors for energizing the two phase coils, a rotor position detector for detecting the position of the rotor based on the induced voltage generated in one phase coil which is not energized when the two phase coils are energized, and a selecting circuit for sequentially selecting the two phase coils of the three phase coils based on the detection result of the rotor position detector. The drive of the motor without sensor further includes a control circuit for turning off the pulse circuit and turning on the source transistor and the sink transistor for energizing the two phase coils according to a signal having a predetermined level when the motor without sensor is started.