A phase control device for use with a voltage-boosting DC/DC converter includes a current sensor for detecting a current flowing through at least one of the primary and secondary windings of a transformer of the DC/DC converter, a ripple determining section for, on the basis of a current signal detected by the current sensor, determining an amount of current ripple occurring when a first switching element or second switching element switches to an ON state, and a phase regulating section for, on the basis of the amount of current ripple determined by the ripple determining section, regulating a phase related to an ON time of each of the first and second switching elements such that the amount of current ripple is reduced to zero.