A gas filled circuit breaker comprises a hermetically sealed tank (1) formed by a surrounding wall (1b) filled with an insulating gas, at least one pair of contacts being arranged inside the surrounding wall. Contact operating means include force generating means which generate a force for operating the contacts and are arranged outside the surrounding wall (1b, 1c), and a rotational shaft (2) connected to the force generating means at the outside of the surrounding wall and extending to the inside thereof so that the force is transmitted through the surrounding wall to the inside thereof. Seal means are arranged between the surrounding wall (1b, 1c) and the shaft (2) to keep a hermetic seal therebetween. At least two bearings support the shaft (2) in a rotatable manner. Connecting means (15) for transmitting the force from the shaft (2) to at least one of the contacts to be moved in relation to the other are connected to the shaft (2) between the bearings.