An estimation unit estimates the amount of power consumption for each unit period of time. A rechargeable battery control unit controls the rechargeable battery such that an exceeding amount of power worth the amount of power exceeding a target amount of power during a unit period of time is charged into the battery, and power is discharged from the battery during a time zone wherein the target amount of power is exceeded, on the basis of the result of the estimation. When the battery needs to be charged in excess of the upper-limit value, the control unit charges the battery up to the upper-limit value during a time zone wherein the amount of power consumption estimated is light, and the amount of power that exceeds the upper-limit value is charged during a time zone that is close to the time zone wherein the target amount of power is exceeded.