To provide a method capable of obtaining a resin molded product sufficiently performing an obtained function without imparting an adverse influence to the function or the performance of a circumferential member or the like without bring about a deformation or the like even when the product is exposed with a high-temperature atmosphere since the product has a sufficient heat resistance, recycling and without imparting an adverse influence to an environment after discarding.

The method for manufacturing the resin molded product comprises the steps of bringing a molten molding material into contact with a gas of a supercritical state, then shaping the material when the molding material containing a polylactic acid as a main ingredient is molten and molded, and cooling the obtained product until the obtained product becomes a glass transition temperature or lower of the molding material under a pressure or lower of the critical pressure of the gas to crystallize the molding material.