An apparatus and method for switching a power transmission mode of a washing machine id disclosed, to prevent malfunction and damages of the washing machine by switching the power transmission mode stably in which the method includes: (a) rotating the cam (600) by driving the clutch motor (60); (b) counting the number of pulses of power supplied to the clutch motor (60); and (c) maintaining the rotation of the cam (600) until the ounted number of pulses is equal to, or greater than a preset number of pulses.