To protect a valve seat part of a uniaxial pressure regulator for tap water from being damaged by high water pressure in water hammer phenomenon.

A stopper for limiting the stroke, is mounted on a plunger of a uniaxial pressure regulator for tap water to control the biting amount of a valve part of the plunger to the valve seat to prevent the damage of the valve seat, and/or a plunger small end valve part is formed in two stages, and a flat part of the valve is brought into contact with the valve seat after the valve is seated, whereby the force is dispersed and the damage of the valve seat is prevented.