To provide a decanter type centrifugal separator which efficiently washes cake in the machine and dewaters the same.

In this decanter type centrifugal separator 10, the bowl has a large diameter cylinder part 20 and the first conical part 21 to the third conical part 23 which succeed from the large diameter end, the first flight 41 of a screw conveyer is extended from the large diameter end of the bowl to the second conical part or the third conical part, a large gap part 41a which is made by enlarging a gap between the tip of the flight and the inner surface of the bowl is formed on the prescribed length region of the terminal part, a cake layer 71 whose section is approximately trapezoid in accordance with a height of the large gap part 41a is formed on the inner surface of the bowl, the cake layer 71 is conveyed by the second flight 42, washing liquid is supplied to the back surface of the large gap part and, thereby, the solid material is washed. Therein, the inclination of the second conical part is set smaller than that of the first conical part and the washing liquid supplied to the cake in the third conical part stirs the cake by means of a cake stirring means 50 which is disposed on the cake conveyance surface side of the screw conveyer of the second conical part.