Abstract: The invention realizes an improved mechanical strainer for fibrous suspensions including: a rotor; a filtering basket substantially coaxial externally to said rotor; an interspace defined between the side surfaces of said rotor and of said filtering basket; an outer casing suitable to house said filtering basket and said rotor. Inside this outer casing there are: a feeding chamber receiving the fibrous suspension to be treated, a delivery chamber of the "accepted" and a waste chamber of the "waste". The rotor is provided with a plurality of diffusing ducts developing through diverging ways according to the flow direction and being suitable to pipe the fibrous suspensions to be treated from said feeding chamber to said interspace.