A valve includes a housing defining therein a channel, a valve seat on an inner surface of the housing at a middle of the channel, a valve body member seated on and unseated from the valve seat to close and open the channel, and a stem spaced from the valve seat and rotatable around a first axis parallel with an opening surface of the valve seat. The valve body member and the stem respectively have a restricting hole and a restricting projection mutually slidably engageable to form a cam mechanism. The cam mechanism, in conjunction with rotation of the stem, reciprocates the valve body member between the seated position and the unseated position, and rotates the valve body member to be in a posture along a flow direction of a fluid flowing through the housing at the unseated position.