PURPOSE: To perform the processing having no sticking of a melting material on the back face by performing a laser beam cutting after fixing in contact by pouring a fluid between the bodies to be worked in case of cutting the body to be worked by overlapping ≥two sheets.

CONSTITUTION: The body 5 to be worked in thin thickness which is overlapped ≥two sheets is fixed by contact-fitting with a clamping device 6 by pouring the liquid 8 of water, oils, etc., therein. THe work having no sticking of melting materials on the back face is performed due to the assisting gas passing through the cut groove smoothly and removing the melting material, when the body 5 to be worked and liquid 8 are cut with the laser beam simultaneously by laser beam 1 in this state.