A mechanism chassis 1 comprises a polygonal flat plate portion 11 for arranging a plurality of mechanisms on a surface of thereof, and a plurality of side plate portions 12, 13, 14, 15 bent from the respective contour sides of the flat plate portion 11 toward a rear side of the flat plate portion 11. The flat plate portion 11 has a high-precision chassis region where those of the mechanisms of which a relatively high precision is required are to be arranged, and a high-strength chassis region where others of the mechanisms are to be arranged satisfactorily with a relatively low precision. The pair of side plate portions adjacent to each other at each corner included in the high-precision chassis region are separated from each other, and the pair of side plate portions adjacent to each other at each corner included in the high-strength chassis region are joined to each other.
