Power transmission device (110) for a noncontact power supply device includes a resonant circuit that outputs an alternating magnetic flux by power from power source circuit (121), and switching elements (112A, 112B) for making the resonant circuit generate an alternating magnetic flux, and transmits power to a power receiving coil of a power reception device by the alternating magnetic flux. Power transmission controller (115) of power transmission device (110) includes a transmission mode of supplying alternating power to the resonant circuit by repeating ON and OFF of switching elements (112A, 112B) by controlling switching elements (112A, 112B). ON time in one cycle of operation of each of switching elements (112A, 112B) used in the transmission mode is a first fixed value. Accordingly, power transmission device (110) in a simplified configuration can be provided.
