To improve the safety of a gymnast at the time of jumping.

Upper and lower boards 11 and 12 to be linked while overlapping rear parts, a compression spring 21 interposed between the front parts of the upper board 11 and the lower board L12 and a regulating board 31 to be linked by respectively overlapping front and rear parts on the lower surface of the upper board 11 and the upper surface of the lower board 12 are combined. The regulating board 31 regulates the oscillating direction of the upper board 11 at the time of step-in rightly downward, prevents the lateral torsion of the upper board 11 and can stabilize the supporting direction of jumping.