1. A breather structure of an in-wheel motor drive unit, comprising:a breather passage provided in a casing that forms an outer shape of the in-wheel motor drive unit;
an entrance port provided at an inlet side of the breather passage, the entrance port connecting with an internal space defined by the casing;
an exit port provided at an outlet side of the breather passage, the exit port connecting with a space outside the casing, an outer side part of the exit port located in an internal space of a wheel for the in-wheel motor drive unit; and
an obstacle standing to form an inner wall of the breather passage and comprising a plurality of barriers, wherein the plurality of barriers are arranged between the entrance and exit ports, each barrier increasing in size from the exit port to the entrance port, the obstacle preventing lubrication oil in the internal space from proceeding straight ahead via the entrance port toward the exit port.