An automotive motor drive unit includes a breather passage (Q) provided in casings (21a, 21r, 22a, 22r) that form an outer shape of the automotive motor drive unit; an entrance port (48m) that is provided at an inlet side of the breather passage and that connects with an internal space (L) defined by the casings; an exit port (67) that is provided at an outlet side of the breather passage and that connects with a space outside the casings; and obstacles (24, 25, 26) standing to form an inner wall of the breather passage and preventing lubrication oil in the internal space from proceeding straight ahead via the entrance port toward the exit port.