To allow a catalyst to be appropriately protected by effectively cooling exhaust gas bypassing a turbine in preventing excessive supercharging by an exhaust turbo-supercharger.

An exhaust bypass passage 8 branching off from the upstream side of a turbine 52 and joining the downstream side of the turbine 52, in an exhaust passage 4, is made to pass through the inside of a cylinder head 7 in its midway. In addition, a valve 82 for opening and closing the exhaust bypass passage 8 is provided in an area 81 of the exhaust bypass passage 8 after passing through the inside of the cylinder head 7. Exhaust gas bypassing the turbine 52 is cooled by engine cooling water circulating inside the cylinder head 7.