To make a belt engaging tool hard to slip off even when the belt loosen by constituting the belt engaging tool by an elastic part which has a fixing part engaged with a fixing and engaging part and can be elastically displaced to a free posture and a dent attaching posture and a belt engaging part which can detachably engage with the belt.

When a belt 6 is to be mounted, both ends of the belt 6 are drawn into an engaging space 24 through a through hole 22 and dangled from the engaging space 24 to under a dent part 20, Next, the both ends of the belt 6 are inserted into a first opening 36 on a belt engaging tool 17 to a second opening 38 and then inserted toward left through a third opening 40 to mount the belt 6 to the belt engaging tool 17. When a tab part 44 is pinched and the belt engaging tool 17 is pushed into the engaging space 24 from the lower side, the elastic part 30 is elastically sunk gradually into the mounting posture. When the belt engaging tool 17 is pushed in to a position where the operation part 34 abuts on the lower end of the cover part 28, a fixing and engaging part 28 is fit into a fixing groove 35 to engage the belt engaging tool 17 to the attaching part 15.