To suppress the inner pressure of a fuel tank from being increased when an automatic stopping mechanism of an oiling gun fails, and concurrently, prevent the occurrence of any danger of the flow-out of fuel when the fuel tank is deformed.

A diaphragm type relief valve 36 is disposed to the outside of the outer cylinder 12 of an inlet pipe 10, and the first port 36A of the relief valve 36 is connected with a communication hole 38 bored at an area to be turned out to be the lower part of a mechanical seal 19. The second port 36B of the relief valve 36 reaches the outer part of a car body, and the third port 36C of the relief valve 36 is connected with an area to be turned out to be the upper part of the mechanical seal 19. When the inner pressure of a tank becomes greater than a specified pressure so as to exceed the valve open pressure of the relief valve 36 while fuel is being fed, the valve body 50 of the relief valve 36 is moved, and the first port 36A is so constituted as to be thereby communicated with the second port 36B.