PURPOSE: To provide a puffer-type small gas circuit breaker by which high circuit breaking performance can be obtained by means of small driving energy by leveling off puffer chamber inside gas pressure different in the magnitude of arc energy in the case of BTF breaking and in the case of SLF breaking.

CONSTITUTION: Contact shoe parts 1 and 2 capable of contacting with/separating from each other are provided in a container filled with arc/extinguishing gas. A puffer chamber 11 composed of a piston 7 and a cylinder 6 is compressed, and the compressed gas is introduced to a nozzle 10 part, and the arc 14 generated between arc contact shoes 4 and 8 is extinguished. A communicating hole 5a is provided in a driving rod 5 to drive a movable part. Plural number of partition 12 to divide a hollow part area equally into a radial shape are provided in a conical shape on the opposite side of the movable arc contact shoe 8 in the vicinity of the communicating hole 5a. Bases of the partition 12 are fixed to the inner wall of the driving rod 5 through a bimetallic member 13 having a low expansion member 13a and a high expansion member 13b.