PURPOSE: To obtain a cupped gauze filter having high reliability by laminating two sheets of the gauzes, projecting high energy density beam along welding line forming three-way edges in flat bag body, forming the flat bag body and forming opening as cupped-state.

CONSTITUTION: The gauzes 1, 2 are laminated and the high energy density beam 23 of light beam from an light beam heating apparatus or electron beam from an electron beam heating apparatus, etc., is applied on these along the welding line 3 for forming three-way edges in the flat bag body 6. Two gauzes 1, 2 are melted, and by shifting this beam 23 along the welding line 3, the welding and cutting are continuously executed at the same time. Welded bead B is formed along the welding line 3 to form the flat bag body 6 opened at one side edge part as the opening edge 5. Successively, the opening edge 5 is opened to form the cupped shape and the cupped bag body 7 is formed. By this method, the cupped gauze filter hardly developing weak position in the gauze and deformation of the net, can be obtd.