To provide an auxiliary device for a mounting-climbing boot for alleviating a foot ache in mountain-climbing because the weight is applied to the feet particularly when descending in mountain-climbing and the tiptoes and the insteps become painful, and even if thick socks, thick insoles, or the like are used to cope with it, an effect is not particularly acquired.

The auxiliary device for the mountain-climbing boot is formed by giving resiliency to a body formed in bow shape conformed to the instep of the foot, providing a plurality of lace insertion portions near the front end of the body, and providing a lace fixing portion at the rear end. The auxiliary device is used mounted on a tongue of the mounting-climbing boot.