The invention discloses a circuit breaker which comprises a shell. An arc extinguishing chamber, an operation mechanism, a tripping mechanism, a first binding post and a second binding post are arranged on the shell. The tripping mechanism is located between the first binding post and the arc extinguishing chamber and comprises a magnet yoke, an armature and a bimetallic strip. The armature is hinged and fixed to the shell through a hinge column. A partition plate for separating the arc extinguishing chamber and the operation mechanism and separating the arc extinguishing chamber and the tripping mechanism is integrally formed on the shell. A torsional spring for enabling the armature to move away from the magnet yoke is further arranged on the hinge column. An included angle is formed at the portion, at the lower end of the bimetallic strip, of the partition plate. The magnet yoke is fixedly arranged inside the shell and provided with a downward-extending elastic presser foot. The lower end of the bimetallic strip is compressed and fixed into the included angle of the partition plate through the elastic pressure foot. By adopting the structure, the circuit breaker is simpler in structure, more convenient to install and better in performance.