The present invention relates to an operating mechanism for a circuit breaker; having an opening means (3) carrying out open-circuit operation by deenergization thereof and a clos­ing means (7) carrying out closing-circuit operation by rotation of a cam (11) caused by deenergization of the closing means so that the opening means conserves energy by deenergization of the closing means and the closing means conserves energy by rotation of the cam; and the operating mechanism according to the present invention is provided with a large gear (8) fixed coaxially with the cam and lacking in teeth in part (8a) and a small gear (9) rotatably driven by a drive source in relation of engaging with the large gear, so that the non-tooth portion of the large gear is provided at the position thereof where the large gear disengages from the small gear just after the closing means completes its energy conservation, whereby the small gear, after completion of energy conservation of the closing means is completed, runs idle in the non-tooth por­tion and the drive source for the small gear is free from pulsation of a load and the drive source smoothly rotates, resulting in that a small drive source is enough for use and the large gear and small gear are not subjected to an over­load, thereby the present invention can provide an operating mechanism of a large current and a large capacity.