A device for measuring the torque of a hairspring for a balance wheel-hairspring oscillator includes an arbor on which a seat is arranged, a benchmark element, pivoting means for pivoting the arbor, means for keeping the outer end of the hairspring fixed relative to the arbor during measurement, elastic elements provided on a portion of the seat, and means for acting on the elastic elements. The inner end of said hairspring is secured to a collet, the diameter of the seat of the arbor is of a dimension to allow a driving connection by friction with the wall of an axial aperture of the collet, and the elastic elements are formed to bring, under the action of the action means, the section of the portion of the seat forming the driving connection from a greater dimension to a smaller dimension than that of the axial aperture of the collet.