The invention concerns a reciprocating linear movement power unit. The powering element consists of a Stirling heat engine and the generator consists of a piston (1) and displacers (2,3) of the heat engine acting as rotors and fixed electromagnetic elements (6) acting as stator. The Stirling engine comprises in a single working chamber (9) at least a piston (1) and two displacers (2,3) such that the assembly is equivalent to two engines working in opposition. The power stroke of one corresponds to the resisting stroke of the other. Preferably, the generator is of the asynchronous type, but it can consist of synchronous assemblies, with variable reluctance or with permanent magnets.