In a valve device for selectively opening and closing a flow passage formed to open on a valve seat by a valve body through a resin-made seat, a hollow portion is formed on either one of the valve body and the valve seat and receives the resin-made seat therein, the resin-made seat has a thickness so that the resin-made seat partly protrudes from the hollow portion, and when the valve body is operated to close the flow passage, the resin-made seat is compressed to bring an end surface of the valve body into contact with the valve seat.