To regulate the turning of a cover at closed and opened positions surely and through simple operation by simple structure, and also easily open/ close the cover.

A turning shaft 23 of a cover 12 is turnably provided around a pivot shaft 19, and also is energized forward by a spring. The engaging condition, between the engaging recess 31 of the cover 12 and the locking projection 32 of a casing 5, is retained by energizing force to regulate turning in a closed position. The abutting condition between the fitting part 24 of the cover 12 and the casing 5 is retained by energizing force to regulate turning in an opened position. When the cover 12 is opened/closed, the cover 12 is moved rearward against the energizing force to release the engaging or abutting conditions, allowing the turning of the cover 12.