A power transmission device that is adapted to transmit electric power to a power reception device by magnetic resonance, comprising: a transmission-side resonance circuit which includes a transmission-side coil (T L) for transmitting the electric power and which has a predetermined reference frequency as a resonance frequency; a class-E amplifier which is adapted to generate and output an alternating-current voltage (V E) at the reference frequency by switching a direct-current voltage fed from a direct-current power source by using a periodic signal at the reference frequency; a selective voltage division circuit which is inserted between the class-E amplifier and the transmission-side resonance circuit and which is adapted to feed the transmission-side resonance circuit selectively with either an output voltage (V E) of the class-E amplifier as a power transmission alternating-current voltage or a voltage (V E ') obtained by dividing the output voltage (V E) of the class-E amplifier as a test alternating-current voltage; a sensing circuit which is adapted to sense an amplitude of a current passing through the transmission-side coil (T L); and a control circuit which is adapted to control the selective voltage division circuit and thereby control a supply voltage to the transmission-side resonance circuit, wherein the control circuit is adapted to acquire, as an evaluation value (V pFOD), a sensed amplitude value from the sensing circuit when the test alternating-current voltage is fed to the transmission-side resonance circuit, and to control, based on the evaluation value, whether or not to perform power transmission by feeding the power transmission alternating-current voltage to the transmission-side resonance circuit. a transmission-side resonance circuit which includes a transmission-side coil (T L) for transmitting the electric power and which has a predetermined reference frequency as a resonance frequency; a class-E amplifier which is adapted to generate and output an alternating-current voltage (V E) at the reference frequency by switching a direct-current voltage fed from a direct-current power source by using a periodic signal at the reference frequency; a selective voltage division circuit which is inserted between the class-E amplifier and the transmission-side resonance circuit and which is adapted to feed the transmission-side resonance circuit selectively with either an output voltage (V E) of the class-E amplifier as a power transmission alternating-current voltage or a voltage (V E ') obtained by dividing the output voltage (V E) of the class-E amplifier as a test alternating-current voltage; a sensing circuit which is adapted to sense an amplitude of a current passing through the transmission-side coil (T L); and a control circuit which is adapted to control the selective voltage division circuit and thereby control a supply voltage to the transmission-side resonance circuit, wherein the control circuit is adapted to acquire, as an evaluation value (V pFOD), a sensed amplitude value from the sensing circuit when the test alternating-current voltage is fed to the transmission-side resonance circuit, and to control, based on the evaluation value, whether or not to perform power transmission by feeding the power transmission alternating-current voltage to the transmission-side resonance circuit.