To create a colorful accessory despite a zirconium oxide substrate being used.

A sintered zirconium oxide substrate 10 is disposed to be inclined relative to a rotational axis direction of a working tool 100, and a recess 12 is formed while the working tool is caused to unevenly contact the zirconium oxide substrate. Furthermore, after the zirconium oxide substrate formed with the recess on the surface thereof is prepared, colored materials are inserted into the recess to give coloring, thus providing an accessory 1 that is given beautiful colors.