An energy supply system comprises an energy supply device (1a) for supplying at least one of electric power and heat, and a controller (6) configured to set first maximum operation time which is an upper limit value of operation time of the energy supply device in a first specified period shorter than a guaranteed operation period of the energy supply device such that operation time of the energy supply device does not reach operation time life before the guaranteed operation period lapses, and calculate and set second maximum operation time which is an upper limit value of the operation time of the energy supply device in a second specified period shorter than the first specified period based on the set first maximum operation time such that the operation time of the energy supply device within the first specified period does not exceed the first maximum operation time.