46 is not limited to the board plank shape but may be variable provided that the structure of the shape can firmly support the other surface of the printed circuit board 30 if the lower hook flaps 45 constructed as above penetrate the penetrating holes 32 of the printed circuit board 30 one surface of the protrusions is in contact with one surface of the printed circuit board 30 while the supporting ribs 46 are in contact with the other surface the printed circuit board 30 thus the printed circuit board 30 is fixed onto the lower hook flaps 45 by a contact of both side surfaces thereof centering around the penetrating holes 32 with the supporting ribs 46 and the protrusions of the lower hook flaps 45 the upper hook flaps 40 and the lower hook flaps 45 are respectively inserted to the slide grooves 31 and the penetrating holes 32 formed on the printed circuit board 30 so as to firmly fix the printed circuit board 30 meanwhile to facilitate assembly of the printed circuit board 30 a guiding slope surface 50 having a slope angle ranged about 5 60 u00b0 is formed on one side of the protrusions as shown in fig9 this means that.