Pressure control valve for controlling operation of fuel injector

A nozzle needle (3) of a fuel injector (10) is driven in a controlled manner by changing back pressure applied thereto. The back pressure is controlled by a pressure control valve (102) driven by stacked piezoelectric elements (51). A valve body (11) of the pressure control valve is disposed in a valve chamber (21) having a drain port (22) and a high pressure port (23) which are selectively closed. A diameter D1 of a drain seat (14), a diameter D2 of a high pressure seat (15), and a diameter D3 of a piston portion (12) connected to the valve body are set to satisfy a relation: D1 ≥ D2 ≥ D3. In this manner, operation of the pressure control valve is stabilized, and thereby the fuel injector is smoothly and stably operated.