A cogeneration system of the present invention includes: an electric power generator (5); a cooling circuit (10) configured to cool the electric power generator (5) with a first heat transfer medium; a heat exchanger (16) provided on the cooling circuit (10); an exhaust heat recovery circuit (12) through which a second heat transfer medium that exchanges heat with the first heat transfer medium via the heat exchanger (16) flows; a heat storage unit (20) connected to the exhaust heat recovery circuit (12) and configured to store the second heat transfer medium that has undergone a heat exchange by the heat exchanger (16); and a controller (21), wherein a first temperature sensor (17), and a heater to which electric power is supplied from the electric power generator (5), are connected, in this order, downstream of the heat exchanger (16) in a direction in which the second heat transfer medium flows, and the controller (21) controls a flow rate of a circulating pump (13) so that, based on a temperature detected by the first temperature sensor (17), the detected temperature becomes a predetermined target temperature. In addition to preventing water temperature decrease in heat recovery and ensuring safety, this configuration can keep water temperature high at all times.