The generator comprises a float (1) which is movable in response to wave motion in a body of water, a submersible reaction member (2) of adjustable buoyancy, with at least two buoyancy configurations, connected to the float and arranged to resist movement of the float caused by the wave motion, an energy converter (5) for converting such reciprocal movement to useful energy; and biasing means such as a spring 6 for directionally biasing the reciprocal movement. Displacement of the float relative to the reaction member is permitted and reciprocal movement generated in response to such displacement.