A grid controller for use in a smart grid system, the smart grid system being configured such that electric power is exchangeable at a point on a power transmission line that connects at least one power generating unit, a plurality of power storage units, and an external power system, each power storage unit including a power storage part storing electric power and a controller performing charge-discharge control of the power storage part, wherein the grid controller is communicably connected to the controllers of the respective power storage units, the grid controller is configured to: obtain transmission power Pall transmitted from the smart grid system to the external power system, the transmission power Pall being a sum of electric power generated by the power generating unit, electric power consumed by loads in the smart grid system, and electric power charged into and discharged from the power storage units; calculate differential power ΔP by subtracting the transmission power Pall from a smoothing operation output Pall', the smoothing operation output Pall' being obtained by performing smoothing operation on the transmission power Pall by using a smoothing filter; and perform control of smoothing the transmission power Pall by performing allocation of the differential power ΔP of the transmission power Pall in accordance with a state-of-charge of each of the power storage parts of the plurality of power storage units, characterized in that the grid controller is configured to: transmit such a control command value as to reduce a charge amount per unit time of a power storage unit whose power storage part is in a charging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a charging state, in a case where the transmission power Pall is less than the smoothing operation output Pall'; and/or transmit such a control command value as to reduce a discharge amount per unit time of a power storage unit whose power storage part is in a discharging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a discharging state, in a case where the transmission power Pall is greater than the smoothing operation output Pall'. obtain transmission power Pall transmitted from the smart grid system to the external power system, the transmission power Pall being a sum of electric power generated by the power generating unit, electric power consumed by loads in the smart grid system, and electric power charged into and discharged from the power storage units; calculate differential power ΔP by subtracting the transmission power Pall from a smoothing operation output Pall', the smoothing operation output Pall' being obtained by performing smoothing operation on the transmission power Pall by using a smoothing filter; and perform control of smoothing the transmission power Pall by performing allocation of the differential power ΔP of the transmission power Pall in accordance with a state-of-charge of each of the power storage parts of the plurality of power storage units, characterized in that the grid controller is configured to: transmit such a control command value as to reduce a charge amount per unit time of a power storage unit whose power storage part is in a charging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a charging state, in a case where the transmission power Pall is less than the smoothing operation output Pall'; and/or transmit such a control command value as to reduce a discharge amount per unit time of a power storage unit whose power storage part is in a discharging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a discharging state, in a case where the transmission power Pall is greater than the smoothing operation output Pall'. transmit such a control command value as to reduce a charge amount per unit time of a power storage unit whose power storage part is in a charging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a charging state, in a case where the transmission power Pall is less than the smoothing operation output Pall'; and/or transmit such a control command value as to reduce a discharge amount per unit time of a power storage unit whose power storage part is in a discharging state among the plurality of power storage units, the grid controller transmitting the control command value to the controller corresponding to the power storage part in a discharging state, in a case where the transmission power Pall is greater than the smoothing operation output Pall'.