Cutter unit for a rotary tiller machine, which comprises a first fixed flange (3) fixed to the rotating driven shaft (2) of the rotary tiller machine, and a second movable flange, mechanically couplable at the front of the first flange (3). Multiple blades (7) are rigidly constrainable to the flanges (3, 4) by means of removable retention means (10) comprising pairs of shaped plates (11, 11"), of which a first plate (11) is provided with two pins (12) projecting from its inner face and a second plate (11") is provided with at least two corresponding holes (13) obtained from its inner face and susceptible of receiving the pins (12). The outer faces of each pair of shaped plates (11) define a slide engageable in a guide (5) obtained between the flanges (3, 4). The coupling portion (7") of each blade (7) is interposed between the pair of shaped plates (11) with the pins (12) arranged to cross through the through holes (14) obtained in the coupling portion (7").A locking pin (15) is provided for each slide, susceptible of crossing through aligned openings (16) obtained on the plates (11, 11") and of removably and mechanically engaging together the first fixed flange (11) and the second movable flange (11").
