Apparatus for monitoring and providing visual representations of the operating conditions of machine tool parameters, in particular for program-controlled turning, milling, and drilling machines, which have a machining unit displaceable in a plurality of coordinate axes, in which a work spindle for exchangeable receiving a machining tool and an electric motor for driving the work spindle are mounted. The machine tool includes a control unit and means for monitoring the operating state of the machine tool. The monitoring apparatus has at least one sensor for detecting at least one operating parameter of the machine tool. An evaluating unit is connected to both the sensor and the control unit and processes the measurement values detected by the sensor. An optical display is provided in the direct viewing range of the operator, which viewing range includes the machine operating spindle, tool holder, tool, and workplace. The optical display can display a normal, a critical, and a dangerous operating state of the machine tool in accordance with the data from the evaluating unit.