Provided is an opening/closing apparatus with a lock capable of performing the opening/closing and closed lock of a sliding door by a single actuator and arbitrarily setting the timing of a lock operation. In the opening/closing apparatus with a lock, an electric motor is driven and the drive force of the electric motor is input to the sun gear of a planetary gear mechanism and output from the internal gear or the carrier. A pair of sliding doors are opened and closed by the drive force output from the internal gear. While the pair of sliding doors are at a fully closed position, the lock and lock-released states of a lock mechanism are switched by a lock restricting mechanism.