A method of manufacturing a molding product of an image sensor unit having a molded product with a substantially rectangular parallelpiped outer shape and incorporating a substrate on which photoelectric conversion elements are arranged in line, includes the steps of forming a frame on the molded product to surround a periphery of the substrate, forming a plurality of caulking projections substantially linearly arranged on an upper surface of the frame in a longitudinal direction, with each caulking projection having a proximal portion extending from the frame, and forming a plurality of antiwarping grooves, with each groove being proximate to one of the caulking projections but spaced apart from its respective proximal portion. Additional steps include fitting the substrate to be fixed in the frame of the molded product, and bending the caulking projections by heat and pressure to fix the substrate in the frame.