A valve unit is connected to a fixed member and an external member. The valve unit includes an actuator to actuate a valve member for communicating and blocking a fluid passage. The valve unit includes a housing defining a chamber therein for absorbing variation in pressure. A mount member secures the housing to the external member. A protruding portion is provided at a location other than a location of the mount member. The protruding portion outwardly extends, thereby being inserted into an insertion hole of the fixed member. A bias member is provided to a substantially annular groove in an outer periphery of the protruding portion. An eccentrically positioning unit positions a bottom surface of the substantially annular groove eccentrically with respect to the insertion hole to bias the bias member to an inner periphery defining the insertion hole.