To provide a cogeneration system which is capable of operating with high efficiency through restraining excessive heat.

A generator selector 36 detects the number of generators which should operate from among generators 10A-10D paged on a power demand and compares the total heat value of the detected number of generators with a heat demand. If the heat demand is smaller than the total heat value, the number of generators matching the heat command are made to operate. If that number of generators is unable to meet the power demand, the balance power is supplemented by power from a commercial power system. If the heat demand is larger than the total heat value, the number of generators matching the power demand are made to operate. If this number of generators is unable to meet the heat demand, the balance heat is supplemented by making the a boiler 37 operate.