The objective of this invention is to reduce the current flowing through the inductance element in a step-up/step-down DC--DC converter and to control the ripple in the output voltage. In the DC--DC converter, four states, that is, the first state [1] of (M1, M2)=(off, on) and (M3, M4)=(on, off), the second state [2] of (M1, M2)=(on, off) and (M3, M4)=(off, on), the third state [3] of (M1, M2)=(on, off) and (M3, M4)=(on, off), and the fourth state [4] of (M1, M2)=(off, on) and (M3, M4)=(off, on) are repeated in a prescribed order, preferably in the order . . . [1].fwdarw.[4].fwdarw.[2].fwdarw.[3].fwdarw.[1] . . . or . . . [1].fwdarw.[3].fwdarw.[2].fwdarw.[4].fwdarw.[1] . . . .