Blood filtering device, particularly for hemodialysis and/or haemofiltration apparatuses, comprising a filter comprising a first compartment, adapted to allow the passage of blood (3, 3'), and a second compartment, said first compartment and said second compartment being separated by a membrane adapted to allow the passage of a filtered fraction from said first compartment to said second compartment, said filtering device comprising an outlet conduit adapted to collect said filtered fraction leaving said filter, said filtered fraction flowing along said outlet conduit along a flow direction, characterized in that said blood filtering device comprises a first sensor comprising: - at least one semiconductor laser source (60, 61) comprising a laser cavity and adapted to generate a laser light beam which strikes said outlet conduit along an irradiation direction incident to said flow direction; - at least one front photodiode (66, 68) placed along said irradiation direction on a side opposite to said semiconductor laser source (60, 61) with respect to said outlet conduit, - at least one lateral photodiode (67, 69) placed along a diffusion direction substantially orthogonal to said irradiation direction, at least in correspondence of said semiconductor laser source (60, 61), of said at least one front photodiode (66, 68) and of said at least one lateral photodiode (67, 69), said outlet conduit being transparent to said laser light beam, said at least one front photodiode (66, 68) generating a first electrical signal dependent on the modulation of the power of said laser light beam operated, according to a retro-injection interferometry effect, by suspended particles present within said filtered fraction and moving along said outlet conduit, said at least one lateral photodiode (67, 69) generating a second electrical signal dependent on the part of said laser light beam which is diffused by said filtered fraction along substantially said diffusion direction; said filtering device comprising a processing and control unit programmed to process said first electrical signal and said second electrical signal to generate a signal indicative at least of the quantity of said suspended particles moving along said outlet conduit. - at least one semiconductor laser source (60, 61) comprising a laser cavity and adapted to generate a laser light beam which strikes said outlet conduit along an irradiation direction incident to said flow direction; - at least one front photodiode (66, 68) placed along said irradiation direction on a side opposite to said semiconductor laser source (60, 61) with respect to said outlet conduit, - at least one lateral photodiode (67, 69) placed along a diffusion direction substantially orthogonal to said irradiation direction, at least in correspondence of said semiconductor laser source (60, 61), of said at least one front photodiode (66, 68) and of said at least one lateral photodiode (67, 69), said outlet conduit being transparent to said laser light beam, said at least one front photodiode (66, 68) generating a first electrical signal dependent on the modulation of the power of said laser light beam operated, according to a retro-injection interferometry effect, by suspended particles present within said filtered fraction and moving along said outlet conduit, said at least one lateral photodiode (67, 69) generating a second electrical signal dependent on the part of said laser light beam which is diffused by said filtered fraction along substantially said diffusion direction; said filtering device comprising a processing and control unit programmed to process said first electrical signal and said second electrical signal to generate a signal indicative at least of the quantity of said suspended particles moving along said outlet conduit.