Abstract: The apparatus includes excitation windings (5, 6, 7) for imparting to an elongate specimen (1) of ferromagnetic material longitudinal oscillations. A device (30) is provided for cutting off a power amplifier (21) of one (5) of the excitation windings, along with a device (28, 29, 30, 32, 33) for detecting and counting the damped oscillations, after the cutting off of the excitation, whose amplitude is greater than or equal to the initial amplitude of the oscillations multiplied by a coefficient so as to permit the determination of the coefficient of internal friction. The excitation winding are constituted by three coaxial cylindrical windings (5, 6, 7) disposed around the specimen (1).