Abstract: A washing apparatus of a screw for extruder including a casing, support rollers installed in the casing so as to support a screw rotatably, a drive motor for rotating the screw, a water jet assembly having a nozzle and nozzle rotation section, a nozzle inclination motor to incline the water jet assembly relative to the axis direction of the screw. A nozzle hole of the water jet assembly is inclined to face one way relative to the axis of the screw placed on support roller assemblies. The nozzle is rotated eccentrically about the nozzle hole and moved from one end to the other of the screw, changing the nozzle hole direction to the other way relative to the screw at the other end of the screw. The screw is rotated so that an unwashed part of the screw faces the nozzle and is washed. This cycle is repeated until the entire surface of the screw is rotated.