Oil mist separation mechanism of internal combustion engine

An oil mist separation mechanism of an internal combustion engine, comprising:

• an oil mist separation portion being integrally provided with an internal combustion engine main body at an outer surface thereof, the oil mist separation portion for separating an oil mist included in a blow-by gas sent from the internal combustion engine main body;
• and
• an oil returning portion being connected to the oil mist separation portion, the oil returning portion returning an oil separated by the oil mist separation portion to an oil stored at a lower portion of the internal combustion engine main body, wherein
• the oil mist separation portion is provided with a turning structure including a first blow-by gas passage portion sending the blow-by gas in a first direction, and a second blow-by gas passage portion being connected to the first blow-by gas passage portion and sending the blow-by gas in a second direction that is opposite to the first direction;
• and
• the first blow-by gas passage portion includes an inlet of the blow-by gas disposed at an end portion of an upstream in a flow direction of the blow-by gas, and the second blow-by gas passage portion includes an outlet of the blow-by gas disposed at an end portion of a downstream in the flow direction of the blow-by gas.