To provide a stain removing method for a waste plastic capable of preliminarily removing stains such as mud or the like bonded to the surface of the waste plastic material by a dry system to prevent the damage of a crusher and capable of reducing the load of water used in wet classification.

A waste plastic material to which a stain is bonded is applied to a crusher not only to be crushed but also to be washed by a dry system to remove the stain. Subsequently, the crushed waste plastic material is sent to a cyclone along with the separated stain to remove the stain. The crushed waste plastic material is returned to the crusher and, on and after, the crushing of the waste plastic material by the crusher, the dry washing thereof and the removal of the stain by the cyclone are repeated. A part of the circulated waste plastic material between the crusher and the cyclone is taken out of a circulating route to be supplied to a sieve to further remove the stain from the crushed waste plastic material.