PURPOSE: To easily produce a mosaic product within a short time by superposing a metal plate having an inlaying thin piece on a through-hole thin plate having a double-coated adhesive sheet bonded thereto and fitting the inlaying thin piece in a through-hole part to prepare a mosaic sheet and bonding this mosaic sheet to a surface to be decorated.

CONSTITUTION: When a detection head 16 reads a pattern 17, the same through-hole part 24 as the pattern 17 drawn on the first manuscript 14 is bored in a perforating thin plate 19 by the laser beam emitted from a processing head 21. The perforating thin plate 19 is bonded to a double-coated adhesive sheet 17. Next, the first manuscript 14 is replaced with the second manuscript to which a plurality of the patterns of the first manuscript 14 are transferred and the perforating thin plate 19 is replaced with an inlaying laminated sheet wherein inlaying thin plates almost same in thickness and a metal plate 12 are temporarily bonded by an adhesive. When the part other than the patterns of the second manuscript is read by a detection head 16, laser beam is emitted from the processing head 21 to form the metal plate 12 having inlaying thin pieces 11. The metal plate 12 is superposed on the perforating thin plate 19 having the double-coated adhesive sheet 7 bonded thereto and the inlaying thin plates 11 are fitted in the corresponding through-hole parts 24 to complete a mosaic sheet.