A fluid pressure cylinder with pressure intensifying function, has an oil-filled hydraulic pressure cylinder which is filled with oil and tightly sealed. A gas-filled gas spring is charged with gas and tightly sealed. By means of gas spring, oil in oil chamber of hydraulic pressure cylinder is pressurized to a pressure level higher than the gas pressure in gas actuating chamber of gas spring. This results in a strong pushing force being generated via output piston of hydraulic pressure cylinder.