Provided is a machining device for machining a rotor arranged in a turbine housing which includes two parts, thereby forming a joint, in situ while the upper housing half is removed. The machining device includes a main part that releasably secures the main part to the lower housing half in the region of the joint, at least one tool holder for receiving at least one machining tool which is secured on the main part directly or indirectly so as to be alignable relative to the main part, multiple telescopic stabilizing elements which can be locked into different longitudinal settings preferably in a continuous manner.