To increase the grounding area of a jumping board auxiliary tool, to restrain sinking in a landing mat on which the auxiliary tool is placed, and to prevent reduction in repulsive elastic force of a jumping board by installing an auxiliary plate on the grounding part front side or the front/rear both sides of the jumping board so as to be freely attachable, and holding the installing state by elastic repulsive force of a rubber cable.

Particularly in balance beam and different level parallel-beam competitions being two events of a female competition, and in a jumping plate auxiliary device used by being placed on a landing mat, an auxiliary plate 1 is provided, and while a cushioning material 5 is stuck to the under surface, a receiving metal fitting 2 to engage with the front part of a lower spring plate 9 of a jumping board 7 is arranged in a upper surface almost central part position. The other end of a rubber cable 4 having a hook 6 on open end is fastened to/installed on a rubber cable installing metal fitting 3 arranged in the receiving metal fitting 2. At using time, a locking state of the receiving metal fitting 2 and the lower spring plate 9 is held by elastic repulsive force of the rubber cable 4 by locking the front part of the lower spring plate 9 of the jumping board 7 on the receiving metal fitting 2 and also locking the hook 6 on the rear end of an intermediate spring plate 8 of the jumping board 7.