Fuel pressure regulation valve

A regulation valve (1) has: a cylinder (20) that has an inlet port (23) at one end side thereof to introduce the fuel thereinto, and a relief port (25) opening on a side face thereof; a piston (21) that is reciprocatably inserted in the cylinder (20) to vary an opening area of the relief port (25) in accordance with a variation of the pressure of the fuel flowing in through the inlet port (23); and a spring (22) that urges the piston (21) in a direction against the pressure of the fuel acting on the piston (21) to regulate the pressure to be a specific value. Further, the cylinder (20) and/or the piston (21) is formed so that the piston (21) opens the relief port (25) at a relatively small speed per a unit displacement thereof in starting opening the relief port (25) and subsequently at a relatively large speed.