To hold positive sealing performance with structure of little fluid resistance and small valve opening/closing stroke, without a principal part being damaged by a fluid.

A glove shaped body part 11 with an inflow port C provided at a lower part and with a main valve seat 11A connected inside, and a cylindrical part 12 with an outflow port D provided at an upper part and with an auxiliary valve seat 12B connected inside, are integrally connected to constitute a valve body 1, and a bottomed cylindrical valve element 21 having an outflow hole 21c at the upper part of a main valve seat 21A is slidably enclosed inside the valve body 1 in such a way as to bring both main valve seats 11A, 21A into contact at the time of closing a valve. The outer peripheral part of the bottomed cylindrical valve element 21, and the inner surface of the valve body 1 are connected to each other through a diaphragm 25 and energized to close by a compression spring 23 at the time of closing the valve. The inflow port side outline of the valve element 21 is formed into conical shape with little resistance, and a plurality of flow straightening grooves 14 are provided along the inner peripheral surface of the body part 11 from the outer peripheral surface of the main valve seat 11A so as to lead a fluid smoothly to the outflow port 21c of the valve element 21 via the main valve seats 11A, 21A in opening the valve.