A pressure-reducing valve 1 includes a tubular valve body 3 movably accommodated in a housing 2, a valve seat 4 fixed inside the housing 2, and an urging member 5 that urges the valve body 3 in a direction separating from the valve seat 4. The valve seat 4 includes an annular elastic member (O-ring 42) capable of abutting against the valve body 3, an annular portion (inner ring portion 41b) that covers an outer periphery of the elastic member, an inner peripheral portion 43b disposed on an inner periphery of the elastic member, a connecting portion (closing plate portion 43a) that connects the annular portion and the inner peripheral portion 43b, and a detachment prevention portion provided in at least one of the inner peripheral portion 43b and the annular portion on a valve body side to prevent the elastic member from detaching from the annular portion.