A device and a method for converting wave motion energy into electric power are described. The device includes at least one support structure and a support frame to connect the floating element to the support structure. A linear element of motive power mounted on the support frame is movable with respect to the floating element and transfers motion to a motion conversion and transmission unit that converts linear motion into rotary motion, which drives kinetic energy accumulation elements and one or more electric power generators. The motion conversion and transmission unit, the kinetic energy accumulation elements and the electric power generators are all incorporated in the floating element.