A method of manufacturing a resin formed product having a leather grain includes: a 3D printing step of inputting printing data to a 3D printer, and printing an intermediate product having an intermediate grain that is a base of the leather grain; and a post processing step of obtaining the resin formed product, which is a finished product, by carrying out post processing on the intermediate product printed in the 3D printing step. A grain height in input data, which is the printing data inputted in the 3D printing step, is greater than or equal to 120% of a stacking pitch in the 3D printing step.