A machining unit for a program-controlled machine tool having a measuring and monitoring device for monitoring the position and condition of a tool shaft in the tool holder. This measuring and monitoring device includes a plurality of axial sensors and radial sensors and an evaluating unit for the measurement results detected by the sensors. An outer ring is releasably fastened to the spindle housing and contains an electronic transmission element and terminals for energy and data cables. A rotor is assigned to this stationary outer ring and contains the sensors and is coupled to the outer ring for the non-contact data transmission. The rotor is releasably fastened to the front end face of the spindle by bolted connections.