There is disclosed a power source system capable of lengthening life and realizing a highly efficient operation while meeting user's needs. The power source system includes a fuel cell which generates power by an electrochemical reaction between a fuel and an oxidizing agent, and a secondary battery which is charged and discharged, wherein the secondary battery is charged by the fuel cell, and the power is taken from the secondary battery. The power source system further comprises a charge control unit which charges the secondary battery with the power generated by the fuel cell, and this charge control unit has a function of switching a mode to charge the secondary battery by the fuel cell in accordance with a frequency with which the power is taken from the secondary battery.