A transmission adapter for a medical instrument with a shaft, a transmission device movable in the shaft, and a manipulating device with a first part, which can be coupled mechanically rigidly to a proximal end of the shaft, and a second part, which is movable relative to the first part, includes a first coupling element for releasable mechanical coupling to the second part of the manipulating device, and a second coupling element for releasable mechanical coupling to a proximal end of the transmission device.