An electric power source in which a plurality of inverters operate on the same frequency and the plurality of inverters are connected in parallel so that a resistance value expressed by (1−β·G)/(α·G) where α is the output voltage feedback gain, β is the output current feed forward gain, and G is the inverter current gain, is made to be the equivalent output impedance; and is an electrical power source in which the cross-current between the inverters are made to be an acceptable value or below by adjusting the output of each of the inverters by controlling the equivalent output impedance by modifying both or either one of the output voltage feedback gain α or the output current feed forward gain β.