To provide a diving fin which has reduced resistance to water in kicking and heightened power saving effect.

In a middle position of a longitudinally long blade 10, a lateral first groove A1 is disposed, and on both sides of the blade 10, a second groove A2 and a third groove A3 are provided respectively along edges of side ribs 101 on both sides of the blade, one end of each of the grooves is extended to both sides of a foot pocket 11 and the other end is linked to both sides of the first groove A2 to form an approximately U-shaped through divided groove A. Then, the blade 10 is divided into a first blade 1021 being a fixed portion and a second blade 1022 being a movable portion.