A system for controlling valve opening/closing timing is configured which allows lock-release operations to be reliably performed. In cases when a lock member is to be extracted from a recess, a second control valve is set in a lock-release position, a first control valve is set in a prescribed position, and the relative rotational phase is displaced. As a result, the relative rotational phase is displaced in a direction opposite to the direction of displacement by cam average torque from a camshaft. Thereafter, the first control valve is set in a neutral position, and, as a result, the relative rotational phase is displaced by the cam average torque. During this displacement, a state in which the lock member is separated from an inner wall of the recess is created, and extraction of the lock member from the recess is facilitated.