To reduce the power required for valve opening by providing such a structure as to move a cylinder inserted into a passage in such a manner as to be movable forward and backward by a flow and block a cylinder outflow port provided on the cylinder by a valve element, and specifying the relation of the opening area of the cylinder outflow port to the passage opening area corresponding to a seal member.

In the application to a washing machine single faucet as a faucet having a valve structure built in a spout, a valve unit 10 consisting of a cylinder 12, a valve element 13, a spring 14, a valve element stopper 16, a bar 18 as cylinder moving means and the like is built in the spout having a passage outlet part 4 for connecting a washing machine connecting member at the tip. When the washing machine connecting member is connected to the passage outlet part 4, the forward and backward movement of the bar 18 is transmitted to the cylinder 12 through a transmitting member to block a cylinder outflow port 35 by the valve element 13 by the force of the spring 14. At this time, when the opening area of the cylinder outflow port 25 is A, and the passage opening area corresponding to a seal member 8 is B, each part is set so that the relation of A>(B-A) is satisfied.