To provide a high separating performance of oil in blow-by gas.

This engine is provided with a lubricating oil tank 1 which is communicated with an oil pan 12 in an engine as well as leading blow-by gas in an engine to an intake passage 21 through a blow-by gas passage 17. The lubricating oil tank 13 is connected to the way of the blow-by gas passage 17, and blow-by gas of the engine is led to the intake passage 21 bypassing an upper space 20 of the lubricating oil tank 13.