Abstract: A device for detecting the unbalance .DELTA.i between the two fractions of the return traction current flowing in the two rails of a railroad track, in the presence of a signalling current in the respective track circuit, includes a linear combination circuit (3) that receives two signals (i.sub.1 and i.sub.2) which are proportional to the two currents actually present in the two rails and obtains both the difference (i.sub.1 -i.sub.2) and the sum (i.sub.1 +i.sub.2) thereof. A demodulating circuit (4), fed with the difference signal, takes from it the modulating signal of the signalling current and feeds it to a sample generator circuit (5), which generates a sample function M(t). The sample function is supplied to two successive sampling circuits (106 and 206), one of which also receives the difference signal and produces a sampled difference signal M(i.sub.1 -i.sub.2), while the other also receives the sum signal and produces a sampled sum signal M(i.sub.1 +i.sub.2).