GAS BREAKER

PROBLEM TO BE SOLVED: To provide a breaker that has a valve structure making a puffer piston compact, and has sufficient breaking performance even with small driving force.SOLUTION: A gas breaker has a movable arc contactor and a fixed arc contactor arranged opposite each other in a sealed container filled with arc suppressing gas. The movable arc contactor is connected to an end of an operation rod while facing the side of the fixed arc contactor. A puffer cylinder is constituted coaxially with the operation rod, and coupled to the operation rod. The puffer piston is inserted into the puffer cylinder to form a puffer chamber. The puffer piston has a compression plate provided with a communication hole linking the interior and exterior of the puffer chamber to each other and a projection part at an inner peripheral part of the compression plate. A valve plate is fitted to the surface of the compression plate on the side of the puffer chamber so as to close the communication hole. The projection part of the compression plate is fitted with a spring receiver, and a coil spring in a truncated cone shape which has a small-diameter-side inner diameter larger than the outer diameter of the projection part of the compression plate is arranged between the spring receiver and valve plate.