A method for producing thermoplastic plastic capable of grasping information concerning the production process even after distribution. In a plurality of production processes including fusion of thermoplastic plastic 90, an information presenting substance 91 is added to the thermoplastic plastic sequentially and dispersed therein in each of the production process, wherein the information presenting substance is associated with information concerning each of the production process and radiates fluorescence upon an irradiation of an electromagnetic wave in a specified wavelength region.