To provide a common rail type fuel injector capable of gradually increasing a fuel injection rate at fuel injection time and capable of suddenly reducing the fuel injection rate at fuel injection finishing time.

In a boosting injector 1, a fuel boosting chamber 19 communicates with a pressure releasing part 3 via a depressurizing passage 11, a recessed part 10, a communicating hole 13, a hollow part 12, and a bypass passage 14. A ball valve 17 arranged in the recessed part 10 cuts off communication of the recessed part 10 and the depressurizing passage 11 at fuel injection time, and communicates the recessed part 10 with the depressurizing passage 11 at injection finishing time. Thus, the injection rate gradually rises at injection time, and since fuel in the fuel boosting chamber 19 flows out to the pressure releasing part 3 at valve closing operation time, an injection port 28 can be quickly closed, so that the injection rate suddenly reduces.