PURPOSE: To provide a pressure-reducing regulator applicable to vehicles, excellent in efficiency, simple in structure, and having a balance valve element device provided with minimum friction drag.

CONSTITUTION: A valve element 44 is positively tied to a diaphragm 64 through an insert 66 supported by the diaphragm 64, and the insert 66 has a flow- accommodating groove formed therein so as to easily generate the instantaneous outlet pressure following a gas supply shut-off. The valve element 44 is balanced in terms of the magnitude and direction of the differential pressure, seating and sealing area in cooperation with an internal structure so as to define a seat 34 arranged with intervals with high pressure and low pressure of natural gas as a boundary and the sealing area, and is maintained in balance regardless of how inlet and outlet gas pressures vary.