To reduce a temperature of a fuel with the raised temperature when the fuel leaks at a fine gap part of a guide part and a slide part in a fuel injection device, provided with a member having a guide part; and a member having a slide part, in which the fuel is injected by driving either one of slide part slidably retained on the guide part.

In the fuel injection device provided with a high pressure fuel inner slide part having the members 11, 50 having the guide parts 12a, 52; and the members 31, 60 having the slide parts 32, 62, the fine gap parts 44, 544 are formed between the guide parts 12a, 52 and the slide parts 32, 62 such that the guide parts 12a, 52 slidably retain the slide parts 32, 62 and the fuel is injected by driving the slide part 32. The device is provided with fuel reservoir chambers 16, 71 communicated with the fine gap parts 44, 544 and circulated with the high pressure fuel; and a cooling device 201 for cooling the high pressure fuel by heat exchange with a cooling medium on a high pressure pipe 23 on the midway of a fuel route for leading the high pressure fuel to the fuel reservoirs 16, 71.