To protect a swimmer by providing a cushion body formed in a flat box type which is open on a lower face, a plumb bob plate stored in the cushion body, and a wear-resistant soft protection sheet and providing them on a bottom face of a pool.

A cushion body 3 is integrally formed by polyethylene foam, polypropyrene foam polyvinyl chloride foam, or polyethylene-styrene graft copolymer foam to hold high impact suction property in a wide scope. Next, a cushion mat for water A is provided with the cushion body 3, a plumb bob plate 4, and a wear-resistant soft protection sheet 5 which is stretched in an opening on a lower face of the cushion body 3. Each mat A is connected on the same face by recessed and projection parts 7 for connection and is provided on a bottom face of a pool. Consequently, even if a swimmer plungs into the pool and hits his head on a bottom part of the pool erroneously, the cushion body 3 achieves cushion function to protect the swimmer.