PURPOSE: To eliminate ununiformed valve opening and prevent any damage to the function of pressure regulation even if a holding body is separated from a movable valve body by making a valve body and the movable valve body of magnetic materials with mutually opposite magnetic poles so as to open a valve seat by the effect of the resiliency of the magnetic force.

CONSTITUTION: A valve body constituting a valve seat member 8 and a movable valve body 9 are made of magnetic materials with mutually opposite poles. As a result, when fuel quantity flowing out to an outlet passage 7 is small, the moving quantity of the movable valve body 9 is also small, and thereat, resiliency due to the magnetic force of the magnetic body is inversely proportional to the moving quantity of the movable valve body 9 so that, except for the time of entirely closing the valve, the valve seat member 8 and the movable valve body 9 face to each other in a non-contact state despite the small moving quantity, so as to secure fluid passage and obtain the stable function of pressure regulation. In addition, even if a holder 10 is separated from the movable valve body 9 during the operation, the bottom surface of a supporting body 15 acts as an auxiliary valve seat and the holding plate 11 of a diaphragm 3 acts as a valve cap, thereby preventing any damage to the function of pressure regulation for fuel.