Abstract: The present invention provides a circuit breaker in which the blast cylinder is delimited by a first cylinder (5) constituting the moving arcing contact, a second cylinder (7) constituting the fixed main contact, and a first piston (14) sliding between said first and second cylinders, said first piston being urged by a spring (17) to come into abutment against a part (16A) fixed to the fixed assembly, the cylinder (5) constituting the moving arcing contact and a tube (16) connected to the fixed assembly and coaxial with said cylinder together delimiting, on the other side of the piston (14) closing the blast cylinder, a variable volume (35, 35B) closed at one end by said first piston (14) and at its other end by an annular end piston (42) connected to said first cylinder (5) and sliding along said tube (16), said volume enclosing said secondary contacts, a first secondary contact (30) being fixed to said tube (16) and the second secondary contact (31) being entrained by said first cylinder (5).