A device for measuring the mass of magnetic material present in an analysis medium, this device comprising: - a generator of an excitation magnetic field for exciting the magnetic material, this magnetic field comprising at least one low-frequency component and one high-frequency component, the low-frequency and high-frequency components corresponding to power peaks in the power spectrum of the excitation magnetic field respectively at frequencies far and f HF, the frequency f HF being strictly greater than the frequency f BF, - a sensor suitable for transforming the magnetic field induced in the magnetic material in response to the excitation magnetic field, into a measurement signal, - a filter suitable for isolating the amplitude of a sinusoidal component of the measurement signal at a frequency mf HF ±nf BF, where m and n are nonzero integers, this filter isolating a new value of the amplitude at each measurement period T m, the temporal succession of the amplitudes isolated by this filter forming an amplitude signal, and - an estimator of the mass of magnetic material present in the analysis medium on the basis of the amplitude signal and of a reference signal which is obtained on the basis of a gauge mass of the same magnetic material measured under the same conditions, characterized in that: - the generator comprises a modulator of the phase of the high-frequency and/or low-frequency component with a modulation signal whose value is modified with a frequency f mod less than or equal to 1/(T m), and - the device comprises a demodulator suitable for demodulating the amplitude of the amplitude signal on the basis of the modulation signal, this demodulator being linked up to the output of the filter and to the input of the estimator. - a generator of an excitation magnetic field for exciting the magnetic material, this magnetic field comprising at least one low-frequency component and one high-frequency component, the low-frequency and high-frequency components corresponding to power peaks in the power spectrum of the excitation magnetic field respectively at frequencies far and f HF, the frequency f HF being strictly greater than the frequency f BF, - a sensor suitable for transforming the magnetic field induced in the magnetic material in response to the excitation magnetic field, into a measurement signal, - a filter suitable for isolating the amplitude of a sinusoidal component of the measurement signal at a frequency mf HF ±nf BF, where m and n are nonzero integers, this filter isolating a new value of the amplitude at each measurement period T m, the temporal succession of the amplitudes isolated by this filter forming an amplitude signal, and - an estimator of the mass of magnetic material present in the analysis medium on the basis of the amplitude signal and of a reference signal which is obtained on the basis of a gauge mass of the same magnetic material measured under the same conditions, - the generator comprises a modulator of the phase of the high-frequency and/or low-frequency component with a modulation signal whose value is modified with a frequency f mod less than or equal to 1/(T m), and - the device comprises a demodulator suitable for demodulating the amplitude of the amplitude signal on the basis of the modulation signal, this demodulator being linked up to the output of the filter and to the input of the estimator.