PURPOSE: To improve a fuel injection quantity with high accuracy and also to prevent inequality of a fuel injection timing and the fuel injection quantity among respective cylinders in the fuel injection device of an internal combustion engine.

CONSTITUTION: A gear 11 is fixed to the rotary shaft 1 of a fuel injection pump, and a gear 21 engaged with the gear 11 is fixed to a sensor rotary shaft 2. A pulse ring 22 is fixed to the sensor rotary shaft 2, and an electromagnetic pickup 3 for detecting the pulse of the pulse ring 22 arranged on a pump main body. A ratio between the number of gears of the gears 11 and 21 is set in such a way as accelerating the rotation of the pulse ring 22 more than the rotation of the rotary shaft 1 of the pump. By this constitution, the pulse number generated per rotation of the rotary shaft 1 of the pump can be increased without increasing the pulse number allotted to the pulse ring 22, and then rotational angle for controlling a fuel injection timing with high accuracy can be detected.