A power system including an electrochemical device, a load device, a power generator, and a charge/discharge controller of the electrochemical device. The electrochemical device includes a positive electrode, a negative electrode, and a liquid electrolyte or a solid electrolyte. The charge/discharge curve of the electrochemical device has at least one step, and a given step of the at least one step has an inflection point. A voltage corresponding to the inflection point or a point adjacent to the inflection point is set as a threshold value, and the charge/discharge controller is configured to control charge/discharge of the electrochemical device such that the voltage of the electrochemical device approaches the threshold value.