A bidirectional DC-DC converter 10 has smoothing capacitors Cs1 and Cs2, a smoothing reactor Ls, resonant reactors Lr1 and Lr2, and a resonant capacitor Cr, as well as insulated gate bipolar transistors (IGBTs) Q1, Q2, and Q3 to which buffer capacitors C1, C2, and C3 are connected in parallel and diodes D1, D2, and D3 are connected in a back-to-back configuration. After part of the energy stored in the smoothing reactor Ls and/or resonant reactors Lr1 and Lr2 draws charges in the buffer capacitor C3 and is stored in the resonant capacitor Cr, the energy is stored in the resonant reactors Lr1 and Lr2. The energy is used to draw charges in the buffer capacitors C1 and C2, achieving soft switching of IGBTs Q1, Q2, and Q3.