System for multiple harnessing and complemented conversion of energy from sea waves, characterized in that it includes a structure of vertical guides along which said central floating body moves, a submerged captive-air tank, held up by said floating body, with the body and the tank so arranged that the movement of the submerged tank is contrary to that of the central floating body, the movement of the central floating body and of the submerged tank being transmitted to said means of conversion of the movement into pneumatic, electrical or hydraulic energy. The system shows high energy harnessing efficiency.