To correspond to the increase of an injection rate following injection of other fluid such as water injection without changing a maximum operation variable of a governor i.e., an operation range by arranging a solenoid valve for presiding feed and shut-off of an operating fluid for a fluid pressure cylinder.

At the time of operation of a diesel engine, when a solenoid valve 8 is closed, feed of air toward a first air chamber 5b of an air cylinder 5 is closed in a condition in which pressurized air is supplied to a second air chamber 5c of the air cylinder 5, the piston 5a of the air cylinder 5 and a regulating screw 11 are displaced in the direction for increasing an injection rate. In this condition, when a governor operating variable is increased, a fuel rack 2 is displaced so as to increase the injection rate, and fuel and water are injected. When water injection is completed and the solenoid valve 8 is switched into an opening condition, pilot air passed through a pilot air pipe 10 is supplied to the first air chamber 5b, the piston 5a is displaced together with the regulating screw 11 in the direction for decreasing the injection rate by a cross sectional difference between the air chambers 5b and 5c, and the fuel rack 2 is pushed back to the direction for decreasing the injection rate.