Abstract: A washing method for a workpiece, a resin molded product and a manufacturing method for a resin molded product. There are three steps involved, a detergent washing step, a rinsing step and a drying step. In the detergent washing step there is an additional step in which the detergent water is separated into a condensed liquid and water vapor, the water vapor being discharged into the air. The apparatus used in the method consists of degreasing baths, and withdrawal baths for the detergent wash, a pure water bath for rinsing and a drying bath. The apparatus also has an air heating unit which supplies hot air to form the water vapor in the separation step of the detergent water.