A power generation system has a power generation unit (1), a casing (2) accommodating the power generation unit (1), a ventilator (3) configured to ventilate the interior of the casing (2), and a first exhaust gas passage (4) configured to pass therethrough an exhaust gas from the ventilator (3) which is discharged out of the casing (2). The first exhaust gas passage (4) merges with a second exhaust gas passage (6) connected to a duct (11) open to outside air before the second exhaust gas passage (6) is connected to the duct (11), the second exhaust gas passage (6) being configured to pass a combustion exhaust gas from a combustion device (5) configured to generate heat to be supplied to a heat load.