PURPOSE: To automatically assemble a sheet metal-made casing constituted by connecting a plurality of panels.

CONSTITUTION: An index table 40, intermittently rotated so as to travel round a plurality of work stations 1ST to 5ST, is installed to arrange a plurality of jigs 45 for holding a panel, which is a constitutional part, with an equal space in the circumferential direction on the index table, and work robots R1 to R5 are arranged in the periphery of the index table corresponding to each work station. In part supply stations 1ST, 2ST, a panel is supplied to the jig 45 by the work robots R1, R2, to hold the panel by a holding means of the jig. When the jig, by rotating the index table 40, arrives at part connecting stations 3ST, 4ST, the panel is connected by the work robots R3, R4. When connecting the panel is ended, the index table is rotated to move the jig to a product take out station 5ST, and a casing, which is an assembled product, is taken out by the work robot R5.