A first pipe, a second pipe and a third pipe are airtightly connected with each other. A cam member rotates about a rotation axis for moving a valve body so as to open/close the first pipe and the second pipe so that the third pipe is selectively communicated with the first pipe and the second pipe, the cam member being movable in a direction parallel with the rotation axis. A cam actuator drives the cam member so as to move the cam member in the direction parallel with the rotation axis to open both of the first pipe and the second pipe, when the cam member is rotated at a predetermined angle.