To provide a new jumping implement for allowing a user to perform jumping movements in a free position, and also to provide an air injecting device for effectively prevent an air leakage even when high inner pressure is generated in a hollow elastic body by jumping.

The implement includes: the hollow elastic body having an upper swelling part, a lower swelling part, and an overflow part connecting the upper and lower swelling parts: and a hard step board having a hole at the center part. The overflow part is inserted to the hole, so as to fix the hard step board to the hollow elastic body. A valve is formed between the lower end of a spring cylinder and a stop board. Thus, the lower end of the spring cylinder is energized toward the stop board by a spring body arranged inside the spring cylinder, and also the stop board is energized toward the spring cylinder by the inner pressure of the hollow elastic body.