A bidirectional DC-DC converter includes: a voltage conversion circuit; a first switch circuit connected between the voltage conversion circuit and a high-voltage DC power supply; a second switch circuit connected between the voltage conversion circuit and a low-voltage DC power supply; a smoothing capacitor provided between the first switch circuit and the voltage conversion circuit; and a control unit. The control unit controls the second switch circuit such that turn-on time of the second switch circuit gradually increases, and thereafter, controls the voltage conversion circuit such that a voltage-boosting switching element of the voltage conversion circuit is turned on and off. After a predetermined time elapses from when the voltage-boosting switching element starts to be turned on and off, the control unit turns off the voltage-boosting switching element and turns on the first switch circuit.