PROBLEM TO BE SOLVED: To completely cut off the communication of a negative pressure source passage with the atmosphere regardless of a pressure operation way.SOLUTION: A straight pipeline 41 and a valve receiving part 42 having a first conical pipeline 47 are provided at a valve guide member 24 and the connection port 45 communicating with the negative pressure source passage 21 is opened to the straight pipeline 41. A plunger 25 having a conical valve part 52 is housed in the pipeline of the valve guide member 24. A cap 26 connecting the head part 53 of the plunger 25 protruded from the first cylinder opening 35 of the valve guide member 24 and the cylindrical part of a valve case member, is provided and a ventilation hole 71 is formed in the skirt part 61 of the cap 26. An annular rib 73 is formed on the bottom of the lid part 60 of the cap 26 so as to surround the plunger 25. When the head part 53 is subject to pressure operation, the annular rib 73 is brought into press contact with the peripheral part of the first cylinder opening 35 to cut off the communication of the first cylinder opening 35 and the ventilation hole 71. By this constitution, the communication of the negative pressure source passage 21 with the atmosphere is cut off.
