A circuit breaker comprises a moving contact 10, a static contact 20, an arc extinction chamber 30 and an electrically conducting plate or arc-striking runway 40 divided into first and second sections by a protruding part 40a directed towards an end of the fixed contact 20. The first section 41 has a free end close to an end of the moving contact and the second section 42 has a free end that extends into the arc extinction chamber. The protruding part is positioned closer to the static contact than any other part of the arc-striking runway. The distance between the static contact and runway may be no greater than the maximum separation of the contacts in a disconnected state. The breaker may comprise a current path 50, which may have an opening located on a side remote from the arc extinction chamber, a gas blowout plate 60, and a removable magnetism-enhancing plate 70, which may be disposed below the runway to form an arc gathering region A between the fixed contact and runway. The runway may further comprise a third section 43 that is connected to the free end of the second section 42 and extends into the arc extinction chamber in parallel.