To transiently vary and control an injection hole area during fuel injection by arranging a projection on a position corresponding to the injection hole on an outer surface of a valve for controlling the injection hole area, and incising the valve leaving a tip end part by at least one slit penetrating a center shaft to constitute freely expandable.

When a seat surface 44 is seated on a seat surface 34 and a valve is closed, power feed is not carried out to an actuator, a lower shaft 7a is pushed down, and a projection part 70 formed on a tip end of a shaft is pushed into a slit 63. A valve 6 is enlarged through a support part 62, and each projection 64 formed on an outer periphery of the valve is brought into linear contact with an injection hole inlet 380 of a hole enclosure. As a result, an injection hole 38 is shielded from an inside completely. After that, when voltage is applied to the actuator and the lower shaft 7a is lifted up, a valve 7 is elastically reverted to a narrow side with receiving spring action by the support part 62 formed on a lower end of the valve, each projection 64 formed on the outer periphery of the valve is separated from the injection inlet 380, and pressurized fuel is injected from the injection hole 38 fully opened.