Blood filtering device , particularly for hemodialysis and/or haemofiltration apparatuses, comprising a filter comprising a first compartment , adapted to allow the passage of blood , 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 (F) from said first compartment to said second compartment , said filtering device comprising an outlet conduit adapted to collect said filtered fraction (F) leaving said filter , said filtered fraction (F) flowing along said outlet conduit along a flow direction (S), characterized in that said blood filtering device comprises a first sensor comprising: - at least one semiconductor laser source comprising a laser cavity and adapted to generate a laser light beam which strikes said outlet conduit along an irradiation direction (R) incident to said flow direction (S); - at least one front photodiode placed along said irradiation direction (R) on a side opposite to said semiconductor laser source with respect to said outlet conduit , - at least one lateral photodiode placed along a diffusion direction (D) substantially orthogonal to said irradiation direction (R), at least in correspondence of said semiconductor laser source , of said at least one front photodiode and of said at least one lateral photodiode , said outlet conduit being transparent to said laser light beam , said at least one front photodiode 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 (F) and moving along said outlet conduit , said at least one lateral photodiode generating a second electrical signal dependent on the part of said laser light beam which is diffused by said filtered fraction (F) along substantially said diffusion direction (D); 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 comprising a laser cavity and adapted to generate a laser light beam which strikes said outlet conduit along an irradiation direction (R) incident to said flow direction (S); - at least one front photodiode placed along said irradiation direction (R) on a side opposite to said semiconductor laser source with respect to said outlet conduit , - at least one lateral photodiode placed along a diffusion direction (D) substantially orthogonal to said irradiation direction (R), at least in correspondence of said semiconductor laser source , of said at least one front photodiode and of said at least one lateral photodiode , said outlet conduit being transparent to said laser light beam , said at least one front photodiode 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 (F) and moving along said outlet conduit , said at least one lateral photodiode generating a second electrical signal dependent on the part of said laser light beam which is diffused by said filtered fraction (F) along substantially said diffusion direction (D); 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 . <EOS>