PURPOSE: To execute washing of grit within one washing tank and to separate and take out the dirty sand and screen scum after the washing.

CONSTITUTION: This grit washing machine is composed of the washing tank 1 to which washing water and the dirty sand are supplied, a lower screw conveyor 3 which is freely turnably disposed in the trough part of the washing tank 1 formed to incline toward the upper part of the tank and is used for transferring the dirty sand, a trough-shaped screen 6 which is disposed in parallel with the upper part of the lower screw conveyor 3 and has a semicircular section and an upper screw conveyor 5 which is freely turnably disposed within the trough-shaped screen 6 and transfers the screen scum captured by the screen upward. As a result, the washing of the grit and the separating and taking out of the grit and the screen scum are simultaneously executed. In addition, chains are not used for the driving section and, therefore, the maintenance is facilitated and the continuous use is made possible.