In a decompression valve, a valve mechanism housed in a body has a valve body that can be seated on a valve seat facing a valve chamber into which high pressure fluid is introduced, and a valve shaft that has one end linked to a pressure receiving member operable in association with pressure of a decompression chamber communicating with a valve hole surrounded by the valve seat and that extends through the valve hole while having the other end facing a back pressure chamber communicating with the decompression chamber, and the valve body is fitted around the outer periphery of the valve shaft. The valve body (36) is fitted around the outer periphery of the valve shaft (35) while allowing circulation of fluid between the valve chamber (32) and the back pressure chamber (65) via a space between the valve body (36) and the valve shaft (35), and an annular seal member (46) present between the valve chamber (32) and the back pressure chamber (65) is disposed between the outer periphery of the valve body (36) and a guide member (30) fixed to the body (16) so as to guide axial movement of the valve shaft (35). Accordingly, it is possible to reduce a number of seal members for providing sealing between a valve chamber and a decompression chamber and thus to reduce the cost.