In a DC-to-DC converter which can convert DC power supplied to a first voltage system circuit, having first and second switching elements, to DC power at a boosted voltage, produced from a second voltage system circuit having third and fourth switching elements, with conversion performed based on control of a switching sequence of the switching elements, the sequence is designed such that switch-off of each of the first and second switching elements occurs only when the current flowing in the switching element is close to zero, thereby suppressing occurrence of voltage surges at switch-off.