A driving force transmitting apparatus is provided with a breather chamber. The breather chamber is defined by a first partition wall, a second partition wall, a third partition wall, an outer wall of a first division casing member and an outer wall of an second division casing. The first partition wall is integrally formed on the first division casing member and extending in a matching direction of the first and the second division casing members. The second partition wall is integrally formed on the second division casing member and extending in the matching direction. The third partition wall crosses the first partition wall and is apart from a common plane of first and second coupling surfaces in the matching direction.