To supply exhaust gas without through a supercharger to an intake side having high pressure, and reduce nitrogen oxides without generating failure on a scavenging pump caused by a component contained in exhaust gas.

In an engine 10, an exhaust turbosupercharger 40 is arranged, a two cycle engine part 20 and a four cycle engine part 30 are compoundly constituted, a turbine 41 of the exhaust turbosupercharger 40 is connected to the two cycle engine exhaust pipe 21 through an exhaust passage 13, a compressor 42 is connected to an intake pipe 11 through an air supply passage 12, and the four cycle exhaust pipe 31 is connected to the air supply passage 12 through a reflux passage 15.