frame 7 have been previously shrinkage fitted into the center shell 23 and the electric motor rotor 8 is inserted in such a state that the end of the center shell 23 adjacent to the frame 7 faces downward the center shell 23 with the electric motor stator 9 the frame 7 and the electric motor rotor 8 in it is placed onto the table 45a to put the concentric assemblage jig 44a into engagement with the concentric assemblage jig mounting surface 7d of the frame 7 and to put the fixed scroll mounting surface 7e of the frame 7 onto the table 45a on the other hand the concentric assemblage jig 44b is put into engagement with the concentric assemblage jig mounting surface 27b of the subframe 27 from such conditions the concentric assemblage jig 44b is vertically slided to insert the subframe 27 into the center shell 23 and the subframe 27 is pressed against the stepped portion 23b by press pins 46 the subframe 27 is fixed to the center shell 23 by means of arc spot welding under these conditions on the assumption that coaxiality of the concentric assemblage jig mounting surface 7d with respect to the bearing 13 perpendicularity of the stepped portion 7c and the fixed scroll mounting surface 7e with respect to the bearing 13 coaxiality of the outer peripheral surface of the subframe 27 and the concentric assemblage jig mounting surface 27b with respect to the bearing 39 perpendicularity of the outer peripheral undersurface at the side of the stepped portion 23b of the subframe 27 with respect to the bearing 39 and coaxiality of the concentric assemblage jig 44b with respect to the concentric assemblage jig 44a fall in predetermined precisions the.