Provided is a gas circuit breaker that can reduce control energy smaller than that in previous double motion systems and an excessive force applied to a moveable pin to achieve a highly reliable double motion system. A gas circuit breaker has a double motion mechanism unit including a driving-side connecting rod, a driven-side connecting rod, a lever to connect the rods, and a guide to define the motion of the driving-side and driven-side connecting rods. A moveable pin extends through a first grooved cam of the driving-side conencting rod, a second grooved cam of the guide, and a third grooved cam of the lever. The driving-side connecting rod operates to move the moveable pin inside the grooved cams. Thus, the lever is rotated, the driven-side connecting rod is driven opposite to the driving-side connecting rod, and the driven-side arcing contact is driven opposite to the driving-side arcing contact.