A small size engine, SD01 has been developed since 1989. For the purpose of cultivating the advantageous properties of the SD01 engine, its cylindrical cam mechanism was modified. The modification was able to operate the Stirling cycle stably and silently. The modified SD01 coupled with an electric motor was reconstructed as a hermetic cooler. The attractive Stirling cooler was evaluated on the conditions of a cooling mode. Moreover, with an aid of the enhanced design concept for the SD01 machine, a small size Vuilleumier machine for heat pump applications was designed and constructed.