To provide a relief valve in which the outflow of excessive cooling medium can be restricted when the relief valve is actuated, and in which a problem of environmental pollution can be eliminated.

A relief valve comprises a metal body 1 provided with a chamber reaching a position of a screw recess part 12a under a male screw, a valve element 8 provided with an opening 6 at the center of a lower surface and engaged with an elastic packing 7 in the opening 6, a compression coil spring 9, and a plate 11 having a through hole 10 at a center are contained in order above a valve seat 3 provided on a bottom part of the chamber, a pressure introducing port 2 is provided under the valve seat 3, and the plate 11 is caulked at an upper part of the body 1 to be fixed, and an orifice 2a is provided at a lower end part of the pressure introducing port 2.