A bidirectional contactless power transfer system comprising a contactless power transfer device (30; 310) that includes a first coil and a second coil spaced apart from the first coil, the bidirectional contactless power transfer system being supplied with electrical power from a primary-side circuit to a secondary-side circuit and from the secondary-side circuit to the primary-side circuit by effect of electromagnetic induction, the primary-side circuit including the first coil, the secondary-side circuit including the second coil, wherein the primary-side circuit in the contactless power transfer device connects to a first power converter (20; 200) having a function to convert direct current into alternating current and a function to convert alternating current into direct current, the first power converter connects to a second power converter having a function of converting direct current into alternating current and a function of converting alternating current into direct current, and the second power converter further connects to a commercial power supply, the secondary-side circuit in the contactless power transfer device connects to a third power converter (40; 400) having a function of converting direct current into alternating current and a function of converting alternating current into direct current, and the third power converter further connects to a direct current power supply, such as a secondary battery, of a moving body, when the power is transferred from the primary-side circuit to the secondary-side circuit in the contactless power transfer device, the second power converter converts alternating current of the commercial power supply into direct current, the first power converter converts the direct current into alternating current to supply the alternating current to the primary-side circuit, and the third power converter converts alternating current output from the secondary-side circuit into direct current to supply the direct current to the direct current power supply of the moving body, when the power is transferred from the secondary-side circuit to the primary-side circuit in the contactless power transfer device, the third power converter converts direct current output from the direct current power supply of the moving body into alternating current to supply the alternating current to the secondary-side circuit, the first power converter converts alternating current output from the primary-side circuit into direct current, and the second power converter converts the direct current into alternating current and supply the alternating current to the commercial power supply, at least one of the first power converter (20;200) and the third power converter (40;400) includes: a switching unit arm including two switching units (Q1, Q2, Q3, Q4) connected in series, each of the switching units being formed of a switching element and a diode connected in inverse-parallel to the switching element; and a capacitor arm connected to the switching unit arm in parallel and including two capacitors connected in series, the primary-side circuit or the secondary-side circuit is connected to a connection point between the two switching units of the switching unit arm and to a connection point between the two capacitors of the capacitor arm, and, if direct current is converted into alternating current, the at least one of the first power converter and the third power converter alternately operates into on and off states in cycles corresponding to a predetermined frequency in accordance with PWM control signals to operate as a half-bridge inverter, and, if alternating current is converted into direct current, the switching elements in the at least one of the first power converter and the third power converter are turned off, only the feedback diodes in the at least one of the first power converter and the third power converter operates and the at least one of the first power converter and the third power converter operates as a voltage doubler rectifier circuit, and bidirectional power transfer is performed only by switching operation of the first power converter, the second power converter, and the third power converter. a switching unit arm including two switching units (Q1, Q2, Q3, Q4) connected in series, each of the switching units being formed of a switching element and a diode connected in inverse-parallel to the switching element; and a capacitor arm connected to the switching unit arm in parallel and including two capacitors connected in series, the primary-side circuit or the secondary-side circuit is connected to a connection point between the two switching units of the switching unit arm and to a connection point between the two capacitors of the capacitor arm, and, if direct current is converted into alternating current, the at least one of the first power converter and the third power converter alternately operates into on and off states in cycles corresponding to a predetermined frequency in accordance with PWM control signals to operate as a half-bridge inverter, and, if alternating current is converted into direct current, the switching elements in the at least one of the first power converter and the third power converter are turned off, only the feedback diodes in the at least one of the first power converter and the third power converter operates and the at least one of the first power converter and the third power converter operates as a voltage doubler rectifier circuit, and bidirectional power transfer is performed only by switching operation of the first power converter, the second power converter, and the third power converter.