Abstract: Machine operating on the Rankine cycle for converting thermal energy into electric energy by making use of low-temperature heat sources for the production of electric energy, comprising a cylinder and a related piston, which a related main shaft is associated to, a direct-voltage power generator, which comprises a rotor and a respective stator and is driven by said main shaft, wherein said cylinder is fed at the head portion thereof through two ports ensuring inlet and exhaust, respectively, by means of a rotating valve provided with at least a through-aperture, which is adapted to enable a flow passage to be established between an inlet conduit and the inner chamber of said cylinder; said rotating valve is driven by a plurality of motion transmission members connected to the main shaft, the latter being in turn connected to the rotor of a power generator.