In a device for recording deformation of a rotor head of a work spindle, at least one magnet is arranged on a stator or a rotor of the spindle, the magnetic field of which penetrates a measurement section of the rotor head, which is traversed by an axial flow of force during clamping of a tool or tool carrier on the rotor head by a tool clamping device arranged in the rotor. The rotor head has a magnetizability or magnetization that varies in the axial direction in its measurement section, and at least one direction-sensitive magnetic field sensor is arranged on the stator radially opposite the measurement section, which is connected to an evaluation device to determine axial deformation of the rotor head as a function of rotation angle from the strength of the magnetic field as a function of rotation angle recorded by the sensor during one revolution of the rotor.