This is a typical construction of a medium voltage, around 13.8 kV, circuit breaker using air as medium. This a draw out type, and the photo shows the contacts at the back of the breaker.
Obviously, this is an old technology type of breaker. Most medium voltage, and even high voltage, circuit breakers today are either oil type, vacuum type or SF6 type. Mediums like oil, vacuum, and SF6 extinguish arcs during switching better than air.