The present invention relates to a fluidic separation device comprising: at least one microchannel (2; 66) extending along a longitudinal axis (X), the microchannel having a cross-section that presents a width measured along a first transverse axis (Y) and a thickness measured along a second transverse axis (Z) perpendicular to the first, the width being greater than the thickness, the microchannel including, along the second transverse axis, bottom and top walls (3 and 4); at least first, second, and third inlets (7, 8, and 9) in fluidic communication with the microchannel (2), the second inlet (8) being disposed on the second transverse axis (Z) between the first and third inlets (7 and 9); and at least first and third transverse separation walls (10 and 11) respectively separating the first and second inlets and the second and third inlets, the first and second separation walls (10; 11) being arranged in such a manner that the second inlet (8) is separated from each of said bottom and top walls (3 and 4) by a non-zero distance measured along the second transverse axis (Z), the second inlet (8) being, in particular, adjacent to at least one of the separation walls.