A cogeneration system of the present invention includes: a fuel cell (1) configured to generate electricity and heat; a hot water tank (2) configured to store hot water having recovered the heat generated by the fuel cell (1); a heat exchanger (7) configured to transfer the heat generated by the fuel cell (1) to the hot water; a hot water passage (8) that is a first heat medium passage configured such that the heat is transferred to the hot water by the heat exchanger (7) and the hot water flows into the hot water tank (2); a heat medium supplier (9) configured to cause the heat medium to flow through the first heat medium passage (8); a hot water supplying passage (11) through which the hot water stored in the hot water tank (2) is supplied to the heat load; an electric power consuming heater (12) configured to heat the hot water flowing through the hot water supplying passage (11) toward the heat load by consuming surplus electric power of the fuel cell (1) and commercial electric power; and a second heat medium passage (A) configured such that the hot water is heated by the electric power consuming heater (12) and flows into the hot water tank (2).