PURPOSE: To form a clean linear pattern on the pattern forming section of a molded part by fitting a masking member on the pattern forming section of the molded part, grinding the pattern forming section along the end periphery of the masking member, and removing the masking member after grinding has been processed.

CONSTITUTION: When a linear pattern is to be formed on the surface of a molded part A, a masking member 13 is fitted onto a space close to a pattern forming section 12. In the second place, the pattern forming section 12 is ground along the masking member 13 by a grinding means 14. After grinding has been processed, the masking member 13 is removed, a linear pattern equivalent to the periphery of the masking member 13 is formed on the pattern forming section 12. A grinding belt is pressed with pressure only on an upper flat section close to the end periphery of the masking member and a curved section where no masking member is fitted on. Since grinding on the molded part is processed in such a way that the curved section is cut off, a clean linear pattern can thereby be formed along the end periphery of the masking member.