The recent progress of several types of power storage devices had made it possible to use them in many categories of our social life as commercial equipments. Simultaneously，activities of research and development about utilization have been more and more active，and several types of integration，such as a hybrid system for vehicles，have been proposed. In power generating categories，several demonstrations have been done，and show the effectiveness of the integration.In this paper，power storage devices are integrated into high-efficient lean-burn engines co-generation in order to improve the operational stability at islanding operation by using the power supplying capability of the power storage device at a maximum，This integration provides both high-efficient power supply by interconnected operation and a stable power supply by islanding operation. And we show the design of control method of gas engine and power storage devices to utilize maximum capabilities of both equipments to derive better performance of the integration