the magnitude and period of the current applied to the motor 2 increase the load of the motor 2 can be determined in accordance with the magnitude and period of the current the controller 10 can obtain the information on the magnitude of the current applied to the motor 2 from the inverter module 6 and can obtain the information on the period of the current applied to the motor 2 from the hall sensor 4 in sensing the period of the current applied to the motor 2 s 1 the period t of the current which is obtained by the hall sensor 4 is compared with the period to of previously set current when the period t of the current which is obtained by the hall sensor 4 is larger than the period to of the previously set current the controller 10 senses the magnitude of the current applied to the motor 2 s 2 in sensing the magnitude of the current applied to the motor 2 s 2 the magnitude i of the current which is obtained by the inverter module 6 is compared with the magnitude 10 of the previously set current when the magnitude i of the current which is obtained by the inverter module 6 is larger than the magnitude 10 of the previously set current it is determined that the load of the motor 2 is no less than a previously set load then it is determined whether a uniform time has passed after driving the motor 2 s 4 when it is determined that a uniform time has passed.