From a viewpoint of the prevention from warming, reduction of CO_2 emissions is called for and the exhaust-heat recovery technology in a factory or a car attracts attention in recent years. Its attention was paid to the free piston Stirling engine with few moving parts as an example of the technology. A linear alternator is used when an output piston takes out the output of the engine which carries out a both-way straight-line motion as electric power. In order for this linear alternator to be operated efficiently, control of an eddy current becomes important. In this research, the lamination method of an electromagnetic plate has been improved, improvement in a generate output was aimed at in the simplest possible form, and the effect was checked in a simulation and an experiment.