To provide a swimming aid for easily accelerating the swimming speed by obtaining great thrust.

This aid is composed of a board 1 to be attached to the sole and an umbrella-shaped body 10 attached to this board 1 so as to be freely opened/closed. The umbrella-shaped body 10 is composed of pole-shaped supporting ribs 11 pivotally supported with a hinge 15 at a receiving part 14 and a sheet 12 stretched over the supporting ribs 11. Over the respective supporting ribs 11, a string body 13 is stretchedly attached for regulating the opening limit of the umbrella-shaped body 10. When the legs are stretched in the water, the umbrella-shaped body 10 is opened and closed and a great thrust can be obtained.