PURPOSE: To provide a liquid filter where clogging of its filter medium is restrained to decrease the work of maintenance of the filter medium.

CONSTITUTION: In a device through which liquid is passed to filter it, a separator 1 which has a filter medium and where liquid is passed through the filter medium to remove foreign matter mixed in the liquid, a filter 5 through which the liquid which had been passed through the separator is passed to remove the residual foreign matter mixed in the liquid, a suction pipe 12 which is open to the air and where part of the liquid which has been passed through the filter medium of the filter is made to flow backward to remove the foreign matter stuck to the filter medium and discharged to outside the filter and a tank 16 for receiving the liquid and the foreign matter discharged from the separator and a backwash type washing body are provided.