Abstract: A single phase induction motor having a main field winding and an auxiliary field winding provided with a phase advancing capacitor is controlled by a control unit having a timer unit and a by-pass switch for by passing the phase advancing capacitor. The main field winding is provided with a main switch operable by a relay controlled by the timer. The control unit also has a clutch detecting unit which detects the engagement and disengagement of the clutch adapted to couple the motor with a load such as a sewing machine. The timer is so set to activate the relay after a predetermined time period when the clutch is disengaged to relieve the motor of its load, whereby the relay causes the main switch to open, and the by-pass switch to close, such that the motor is operated solely on the auxiliary field winding when no load is applied, so as to save the power consumption at an idling operation.