PURPOSE: To prevent the reduction in assemble workability by providing a buffer elastic material between an upper plate and a lower plate of a buffer member for fixing mechanism part, and by connecting an undercover buffer material to the lower plate through a screw, with the cover sandwiched.

CONSTITUTION: A buffer rubber member 4 is sandwiched between a buffer material upper plate 3 and a buffer material lower plate 5, and is baked, so as to form a buffer material 9 for fixing mechanism part. An under-cover buffer material 6 is arranged below a base cover 2, while the buffer material 9 for fixing mechanism part is arranged above the base cover 2. A mechanism part fixing screw 8 is connected to the buffer material upper plate 3, while an under- cover buffer material fixing screw 7 is connected to the buffer material lower plate 5. The reduction in assembly workability can thus be prevented.