A rotary valve apparatus includes a casing having a fluid passageway, a rotor rotatably mounted in the casing and configured to control, by rotation thereof, a flow state of fluid flowing in the fluid passageway, a drive mechanism for rotating the rotor, and a lock mechanism configured to allow transmission of a rotational force from the drive mechanism to the rotor and to inhibit rotation of the rotor under non-rotation driving state of the driving mechanism.