Abstract: An electric chuck constituted by an electric motor coupled to a chuck in which the rotating tool is engaged; the electric motor being provided with a cooling device for the rotor located within the interior of the casing of the electric motor; the cooling device being constituted by an annular heat sink fitted to the shaft of the rotor in contact with the armature of the rotor, and a calibrated nozzle for directing a jet of air over the annular heat sink; the chuck being provided with a release device for the rotating tool operated pneumatically and controlled by a source of air under pressure, and the said calibrated nozzle being connected to this source of air under pressure.