Provided is an oil separator wherein each of multiple oil separation units uniformly traps the oil mist in blow by gas regardless of differences in the particle diameter thereby efficiently separating the oil mist and enabling efficient operation of the entire oil separator. This oil separator is equipped with: a distribution chamber that distributes blow by gas; an inflow hole through which blow by gas is introduced into the distribution chamber; at least one oil separation unit which is arranged symmetrical with respect to at least one plane that includes an axis passing through the axial center of the inflow hole of the axes of the directions of circulation of the blow by gas flowing into the distribution chamber through the inflow hole; and branch passages that individually circulate the blow by gas from the distribution chamber to each oil separation unit.
