PURPOSE: To provide a compact relief by which a relief operation characteristic can be stabilized and a buffer action can be exhibited reliably even when an initial pressure is particularly comparatively high.

CONSTITUTION: A small diameter orifice 60 is arranged in an oil passage 52 to introduce pressure oil in a high pressure chamber 10 to a main poppet back chamber 42, and an annular orifice is formed in an oil passage 54 between the main poppet back chamber 42 and an outer diameter part of s rod part 18. The small diameter orifice is formed so as to have a throttling effect sufficient to hold stably a main poppet 14, and on the other hand, the annular orifice is set so as to obtain a necessary/sufficient throttling effect.