A sliding surface 4A of a shoe 4 undergoes laser radiation in a shape of a large number of parallel lines to form a large number of swollen portions 6 and concave portions 7 in adjacent positions thereof. The swollen portions 6 and the inner side thereof become direct-hardened portions 11 with a high hardness and the concave portions 7 and the inner side thereof become double-hardened portions 12, which are lower in hardness than the swollen portions 6. After the laser hardening, the sliding surface 4A undergoes lapping up to a position of an imaginary line 15 to delete the relief and form a flat and smooth plane. Thereafter the sliding surface 4A undergoes buffing so that portions with a low hardness are chipped off more than portions with a high hardness to form a large number of minute irregularities on the sliding surface 4A.