A housing has a housing main body that defines an internal space therein, an inlet port that fluidly connects the internal space and an outside of the housing main body to each other, and a relief port that fluidly connects the internal space and the outside of the housing main body to each other. Coolant water flows into the housing through the inlet port. A relief valve is disposed in the relief port and configured to selectively allow and block fluid communication between the internal space and the outside of the housing main body via the relief port by selectively opening and closing the relief port in accordance with conditions. A valve has a valve body rotatable about a rotation axis in the internal space, and a shaft disposed along the rotation axis. A covering portion is configured to cover the relief valve not to be visible through the inlet port.