An energy supply system includes: an energy supply device (1a) configured to supply electric power and/or heat; and a controller (6) configured to set a first maximum operation time of a first specified period including a plurality of second specified periods, the first maximum operation time being an upper limit of an operation time of the energy supply device in the first specified period; calculate and set a second target maximum operation time of each of the second specified periods of the first specified period such that the operation time of the energy supply device in the first specified period does not exceed the first maximum operation time, the second target maximum operation time being a target value of an upper limit of the operation time of the energy supply device in the second specified period; and reconfigure the second target maximum operation time of a future second specified period of a certain first specified period based on a time in which the energy supply device has been actually operated in a past second specified period of the certain first specified period.