To produce a highly efficient operation and zero fluid stay and to produce a high leakage prevention mechanism.

A flange 128 for sectioning and forming an outer diameter termination edge of a poppet valve element 32 has a tongue part 132 projecting in the axial direction from the flange 128. A diaphragm 34 extends in the radial direction around the head part of the poppet valve element 32 and interposes between the heat part of the poppet valve element 32 and the flange 128 so that the head part of the poppet valve element 32 with regard to the flange 128 may be operated. The head part of the poppet valve element 32, the flange 128 and the diaphragm 34 are an integrally structural member. This assembly is provided with a circular valve seat 36 located adjacently and oppositely to the poppet valve element 32. The valve seat 36 has a poppet valve element contact surface 40 inclined in an upper direction toward a radial inward direction in a radiation axis line direction of the valve seat 36 in the range of about 2 to 30 degrees. The surface of the poppet valve element 32 and the surface of the valve seat 36 act each other and perform seating and non-seating operations of the assembly. On a contact surface of the poppet valve element 32 and the valve seat 36, unnecessaries are swept.