An air conditioner compressor united with a starter motor includes: a drive portion including a motor and a drive shaft, a refrigerant compressing portion for compressing a refrigerant by a rotational force of the motor driven by a battery power source applied through a compressor relay, a power transmission device for transmitting a rotational force of the drive shaft to an engine crank shaft when the motor is driven, and a clutch device for controlling the rotational force between the drive shaft and the power transmission means. The motor and the clutch device are connected to a starter relay and receive the battery power source when starting an engine such that the motor and the clutch device operate when the starter relay is turned on to transmit the rotational force to the engine crank shaft through the drive shaft and the power transmission device, thus starting the engine.