A triangular-wave current flows through a reactor of a DC/DC converter for converting voltages between increased and reduced levels. Surges are reduced, which are developed in an output voltage serving as a control voltage when the triangular-wave current changes across a zero value at which the current direction is changed. When a primary current flowing through the reactor changes across 0 [A] (zero value) at which the direction is changed, within an adjustment range, a feedback coefficient by which to multiply the error between the control voltage and a target voltage is multiplied by k (k>1) so as to increase a feedback amount. Surges developed in the control voltage due to a dead time when the primary current changes across 0 [A] are reduced.