To enable precisely recovering a polystyrene without using a separating liquid which causes an ensuing corrosion and the consequent generation of a harmful gas and bringing about the lowering of processing efficiency.

This method for sorting discarded synthetic resins comprises a wet separation process for separating the crushed scraps of the discarded synthetic resins including the polystyrene and at least one or more kinds of other synthetic resins excepting the polystyrene into the first crushed scrap with a specific gravity of 1 or more including the polystyrene and the second crushed scrap with a specific gravity of 1 or less, using a difference in specific gravity in water with the help of a wet separation device 1 and a dry separation process for recovering the polystyrene crushed scrap from the first crushed scrap using a. difference in friboelectric polarity of the synthetic resin with the assistance of a dry separation device 20.