Provided is an oil separator that operates in an efficient manner as a whole for collection of oil mist in blowby gas as multiple oil separator units collect the oil mist equally regardless of various particle sizes thereof. The oil separator includes a distribution chamber distributing blowby gas, an introducing hole introducing the blowby gas into the distribution chamber, at least one set of oil separator units disposed in symmetry relative to at least one plane having an axis extending through an axis of the introducing hole of axes of flowing directions of the blowby gas entering the distribution chamber through the introducing hole, and distribution channels causing the blowby gas to flow from the distribution chamber to the respective oil separator units.
