Disclosed is a DC-DC power conversion apparatus (10) including two or more switching units (SU1, SU2) each of which further includes two semiconductor switching elements (Sa, Sb), and wherein each of the semiconductor switching elements (S1a, S1b, S2a, S2b) of each of the switching units are all connected in series, and which also includes an energy transition capacitor (C1) for conducting charging/discharging, and an inductor (L). The DC-DC power conversion apparatus (10) is also provided with a control unit that makes the semiconductor elements execute operations in four types of switching modes, according to the ratio (V2/V0) of the input/output voltages of the power conversion apparatus and the direction of the power transmission, and that also makes the elements carry out a current-discontinuing operation wherein the inductor current will become zero during switching operation, upon low load.