182 are joined with the side wall 253 on the side portions of the frame cover 1 b the upper ends of the vertical ribs 181 are not coupled to the side wall 253 this is because the upper portion of the frame cover 1 b needs sufficient space to accommodate thread cassettes and an led display substrate the spaces surrounded by pairs of intersecting vertical ribs 181 181 and horizontal ribs 182 182 form approximately square or rectangular shaped cells 183 hence a plurality of cells 183 are formed on the back side of the front panel wall 252 among the cells 183 the outside wall reinforcing rib 180 defining a cell 183 having a wider area is formed to have a higher height from the front panel wall 252 compared to a cell 183 having a narrower area the outside wall reinforcing rib 180 on the accommodating part for the stitch forming mechanism in the arm 6 or the bed 8 has a lower height from the front panel wall 252 than those of the outside wall reinforcing ribs 180 on the inside of the front panel wall 252 other than the accommodating part the cells 183 in the vicinity of the accommodating part for the stitch forming mechanism have narrower areas than those of the cells 183 provided on the area other than the accommodating part the reason the above arrangement has been adopted is the same as that of the main frame 1 a so that detailed explanation will be omitted the above arrangement of the outside wall reinforcing rib 180 ensures the sufficient rigidity of the front panel wall 252 thereby minimizing or.