To obtain a disc-shaped or cylindrical part made of a synthetic resin of high precision.

A plurality of pin-shaped parts 12, arranged concentrically with the axial line o of parts at least at one side surface 11 of the disc-shaped or cylindrical part 10 made of the synthetic resin formed by injection compression molding in a state concentric to the axial line o of the part are compressed until the heads 12a of the pin-shaped parts 12 reach the same surface as one side surface 11 in a compression process at the time of injection compression molding or reach a position where projecting parts 11a are formed to one side surface 11 within the range of an error ΔL in the compression process.