PURPOSE: To close the unused section of a groove and enhance the appearance design by internally providing the groove with a lid member energized forward for closing the open section thereof where an attachment is engaged.

CONSTITUTION: A groove member 1 has a T-slot 2 recessed over an entire lengthwise direction, and a lid member 3 is laid in the slot 2. Furthermore, the member 3 is formed out of a plate type section 4 engaged with the inner side of the groove 2, and a row 6 projected from the plate section 4 in a lengthwise direction, so as to close the narrow opening 5 of the T-slot 2. The opening 5 of the T-slot 2 is closed with the projected row 6 on the action of a plurality of coil springs 8 laid in a spring hole 7 on the bottom of the T-slot 2. in addition, the head 13 of a T-stud 12 in an attachment has a recess 13a for engagement with the row 6 of the member 3. The head 13, while being directed parallel to the T-slot 2, is inserted therein, pushing away the member 3, and then, turned by 90 degrees, thereby aligning the recess 13a with the row 6.