A fuel injection valve comprising: a body having a high pressure fuel passage, through which high-pressure fuel flows, and a nozzle hole, which is connected to the high pressure fuel passage; a nozzle needle disposed to open and close the nozzle hole and having a needle piston part; a piezo stack configured to be extended when the piezo stack is charged with electric charge and configured to be contracted when the piezo stack discharges the electric charge; and a cylinder, in which the needle piston part of the nozzle needle is slidably inserted and which is driven by the piezo stack; characterized in that said fuel injection valve further comprises: a fixed piston fixed to the body and having a fixed piston part, which is slidably inserted in the cylinder, wherein a diameter of the fixed piston part is larger than a diameter of the needle piston part; an oil-tight chamber defined by the needle piston part and the fixed piston part and located between the needle piston part and the fixed piston part in the cylinder; and a nozzle spring disposed to urge the nozzle needle in a direction in which the nozzle needle closes the nozzle hole, wherein: the cylinder is displaced as a result of the extension of the piezo stack, so that volume of the oil-tight chamber increases and thereby the nozzle needle opens the nozzle hole; and the cylinder is displaced as a result of the contraction of the piezo stack, so that the volume of the oil-tight chamber decreases and thereby the nozzle needle closes the nozzle hole. a body having a high pressure fuel passage, through which high-pressure fuel flows, and a nozzle hole, which is connected to the high pressure fuel passage; a nozzle needle disposed to open and close the nozzle hole and having a needle piston part; a piezo stack configured to be extended when the piezo stack is charged with electric charge and configured to be contracted when the piezo stack discharges the electric charge; and a cylinder, in which the needle piston part of the nozzle needle is slidably inserted and which is driven by the piezo stack; characterized in that said fuel injection valve further comprises: a fixed piston fixed to the body and having a fixed piston part, which is slidably inserted in the cylinder, wherein a diameter of the fixed piston part is larger than a diameter of the needle piston part; an oil-tight chamber defined by the needle piston part and the fixed piston part and located between the needle piston part and the fixed piston part in the cylinder; and a nozzle spring disposed to urge the nozzle needle in a direction in which the nozzle needle closes the nozzle hole, wherein: the cylinder is displaced as a result of the extension of the piezo stack, so that volume of the oil-tight chamber increases and thereby the nozzle needle opens the nozzle hole; and the cylinder is displaced as a result of the contraction of the piezo stack, so that the volume of the oil-tight chamber decreases and thereby the nozzle needle closes the nozzle hole. a fixed piston fixed to the body and having a fixed piston part, which is slidably inserted in the cylinder, wherein a diameter of the fixed piston part is larger than a diameter of the needle piston part; an oil-tight chamber defined by the needle piston part and the fixed piston part and located between the needle piston part and the fixed piston part in the cylinder; and a nozzle spring disposed to urge the nozzle needle in a direction in which the nozzle needle closes the nozzle hole, wherein: the cylinder is displaced as a result of the extension of the piezo stack, so that volume of the oil-tight chamber increases and thereby the nozzle needle opens the nozzle hole; and the cylinder is displaced as a result of the contraction of the piezo stack, so that the volume of the oil-tight chamber decreases and thereby the nozzle needle closes the nozzle hole. the cylinder is displaced as a result of the extension of the piezo stack, so that volume of the oil-tight chamber increases and thereby the nozzle needle opens the nozzle hole; and the cylinder is displaced as a result of the contraction of the piezo stack, so that the volume of the oil-tight chamber decreases and thereby the nozzle needle closes the nozzle hole.