To easily and continuously achieve the flow rate control of fluid without generating any variation.

A pressure chamber 2 communicated to the channel of pressure fluid is provided with a plunger 6 acting like a piston according to the pressure, and a needle valve-shaped valve body 6 is operated by the plunger 6. The plunger is put to have a relation that the pressurizing force of a coil spring 8 is balanced with the pressure or negative pressure of the pressure chamber, and the opening of the valve is adjusted by an adjustment screw 9. The relation of the opening of the valve body by an adjustment screw and a pressure balanced therwith is preliminarily confirmed, and a fluid inlet 3 is connected to a fluid supply source to be introduced, and a fluid outlet 4 is connected to the channel of pressure fluid, and the opening of the valve body is set by an adjustment screw. When fluid is supplied from the valve body opened by the pressure of the channel and the pressurizing force of the coil spring, the channel pressure is decreased or increased, and the opening of the valve body is controlled until the opening of the valve body is adjusted against the pressurizing force of the coil spring according to the pressure change, and continuously put in a balanced state.