The gas circuit breaker is made up of a fixed contact, a movable contact, a sealed tank having the fixed contact and the movable contact therein, an operating mechanism for driving the movable contact, and a mechanism unit for housing a link mechanism for connecting the operating mechanism with the movable contact. The operating mechanism is made up of an opening spring and a closing spring, cases for covering respective peripheries of those elastic bodies, a control mechanism for holding and freeing the driving force of the elastic body, and a link mechanism for conveying the driving force of the elastic body to the movable contact. The opening spring is laterally disposed in the axial direction between the link mechanism and the control mechanism. An integral flange is provided on an opening spring case and a closing spring case.