1. A power system management device configured to manage a system state in a power system, comprising: a system state candidate calculation unit configured to calculate a plurality of state amounts of the system state based on a predetermined objective function from system characteristic information indicating characteristic information of a system structure including a load, a device, or a power transmission line connected to the power system; an inter-state distance calculation unit configured to calculate an inter-state distance representing a similarity of values between the plurality of state amounts of the system state which have been calculated by the system state candidate calculation unit; and a variability evaluation value calculation unit configured to calculate a variability evaluation value in which a variability of each system state is evaluated, based on an objective function value which is calculated from the state amount of the system state which has been calculated by the system state candidate calculation unit and the inter-state distance which has been calculated by the inter-state distance calculation unit, wherein the system state is selected based on the variability evaluation value calculated by the variability evaluation value calculation unit.