A power system apparatus that suitably secures users of electric vehicles performing charge/discharge at the timing when power supply/demand adjustment is needed is provided. The power system apparatus disclosed herein includes: a power supply/demand information acquisition unit; a first calculator configured to calculate an urgency degree or a redundancy degree and a first rank point; a communication unit; a charge/discharge management unit; a second calculator configured to acquire a charge/discharge amount and calculate a second rank point; a rank setting unit configured to set a rank based on the first rank point calculated by the first calculator and the second rank point calculated by the second calculator; and an incentive management unit configured to calculate an incentive.