A separation portion of an oil separator is located upward from an opening of a second blow-by gas passage portion in an outer surface of a cylinder block. A connection passage connects the separation portion and the second blow-by gas passage portion. At least part of the connection passage located toward the second blow-by gas passage portion serves as a first passage portion. The second blow-by gas passage portion and the first passage portion serve as an intermediate passage. A step is arranged in the intermediate passage at an intermediate portion with respect to an extension direction of the intermediate passage.