An automatic tool-exchanging apparatus is provided which extends/contracts an arm with a rational and simple structure and can realize a high-speed operation essentially obtainable by making the arm's turning radius small. The apparatus comprises: an arm-driving shaft for being driven to rotate; an arm provided on the shaft and capable of being rotated, the arm capable of being moved to extend/contract and comprising a grip arm for attaching/detaching a tool, and an arm support movably supporting the grip arm; a clutch between the arm support and the shaft, the clutch for connecting the arm support and the shaft to make them rotate integrally, and disconnecting the arm support and the shaft to generate a relative rotation therebetween; and a link between the grip arm and the shaft, the link for transmitting the relative rotation of the shaft in respect to the arm support to make the grip arm move.