A fuel cell system includes: a fuel cell (1) configured to generate electric power by a reaction between fuel and an oxidizing agent; a cooling passage (3) through which a first heat medium for cooling down the fuel cell (1) flows; a heat exchanger (5) disposed on the cooling passage (3); and an exhaust heat recovery passage (7) through which a second heat medium which exchanges heat with the first heat medium by the heat exchanger (5) flows, wherein a deceleration portion (7c) configured to reduce a flow velocity of the second heat medium and a bubble release portion (7d) configured to discharge bubbles in the deceleration portion (7c) to an outside of the exhaust heat recovery passage (7) are disposed on the exhaust heat recovery passage (7).