PURPOSE: To obtain a backwashing device of filter capable of perfectly backwashing a filter body by using a gas from a low-pressure gas source, by providing a gas tank and a valve to the midway between a compressed-gas source and the filter body, and setting the diameter of a backwashing pipe between the valve and the filter body larger as compared with that of a gas distributing pipe.

CONSTITUTION: A compressed gas source 1 is connected to a gas tank 3 by a gas distributing pipe 2, and the tank 3 and a filter body 6 are connected by a backwashing pipe 4 through a backwashing valve 5. The diameter of the pipe 4 is made far larger than that of the pipe 2. Accordingly, a gas in the tank 3 can be discharged in a few seconds from the whole surface of the body 6, and it shows an excellent backwashing performance. This gas-backwashing device is mainly used for a liquid, especially for an oil filter, and air is usually used as the compressed gas. Further, in the figure, 7 shows an assembling pipe, 8 and 9 show a liquid level and an oil storing tank, respectively.