To ensure safety when a user vaults over a buck by preventing escaping or floating-up of one or more of buck constituting frames through the connection therebetween or the provision of a pressing board that presses a lowermost step frame upper edge surface.

Adhesive is applied to an outer surface of each step of frame 1 of a buck, and adhesive superposedly adhering to the former is applied to a rear surface of a cushioning member 4. The member 4 is bonded to a buck frame 1 connection part through these adhesives to thereby prevent escaping between the respective buck frames 1. Otherwise, instead of the adhesives, an engagementwise connection by use of loking fittings and a locking part such as locking rod are used. Also, a retaining plate may be used to press an upper edge surface of the lowermost step buck frame 1 so as to prevent floating up of the buck fame 1.