than that of the electric double layer capacitor 3 as a result the total output of the gas engine generator 1 and the nickel metal hydride battery 2 has an output shown as the reference symbol b 3 since the output of the electric double layer capacitor 3 changes to perform the charging operation after the discharging operation so that the total output of all power sources matches with the load electric power reference symbol b 4 the soc of the electric double layer capacitor 3 can be recovered in other words it is possible to rapidly recover the remaining capacity of the electricity storage device the electric double layer capacitor 3 by increasing the output of the power source the nickel metal hydride battery 2 except for the electricity storage device than the load electric power after discharging the electric power from the electricity storage device the electric double layer capacitor 3 next results of the operations when the soc management control is performed and when the soc management control is not performed will be described with reference to fig4 a and 4b fig4 a illustrates a result of an operation when the soc management control is not performed fig4 b illustrates a.