The invention relates to a method and apparatus for gradually converting marine wave energy into electricity. The energy reserve provided by wind power holds enough energy for the needs of the entire mankind. The invention provides an efficient means of putting this energy reserve to practical use. Mounted on a rotating power shaft (3) is a pair of form parts (1, 2), the convex and concave shape, especially the round-pointed open V-shape of which reverses its orientation by 180 degrees, i.e. turns from convex to concave, whenever the power shaft makes a rotation of 180 degrees. The circular motion of water occurring in a wave drives such a turbine effectively while the wave dies out. The pair of convex and concave form parts (1, 2) extends helically around the power shaft (3), whereby water currents in all directions, which come to contact with the pair of form parts, produce a rotative moment.