To omit arrangement of a mud receiving pit (an opening place receiver) and a side-ditch required so far when arranging a greaser trap.

A grease trap is partitioned into first, second, third three chambers by using a partition plate, and the first chamber has a net basket for separating an impurity in polluted water and a mud separating tank for separating mud under the net basket. Then, the second chamber floats and separates the fat and oil content of the polluted water from which mud of an impurity is removed in the first chamber, the third chamber has a trap pipe for making fat and oil content-separated fresh limpid water flow outside a vessel and an inclined side-ditch cover plate successively inclined in a lowering state toward the second chamber and the first chamber from the third chamber side is installed above the second chamber and the third chamber. In the mud separating tank, a cylinder is erected in the center of the tank bottom, an umbrella hat body is installed in an upper part of the cylinder, the inside of the cylinder is bottomless to be put in a state of communicating with the bottom surface side of the first chamber 1, the mud of sludge flowing down from the upper net basket gathers on the tank bottom, and a polluted liquid overflows from the cylinder upper edge.