A rectilinear channel (36) which is open upwards to be loaded with material to be processed, and has an inlet mouth (36a) and an outlet mouth (36b) at its opposite longitudinal ends. A perforated, rectilinear tube (30) is aligned to the rectilinear channel (36) and has an open inlet end (30a) connected to the outlet mouth (36b) of the horizontal channel (36), as well as an open outlet end (30b). Shutting means (49, 146) are connected to first piston driving means (50, 148), which are operable to close the outlet end (30b) of the perforated tube (30). A pressing member (40) is slidably insertable through the inlet mouth (36a) of the channel, under control of second piston driving means (42), to progressively enter the channel (36), in such a way as to push the material contained therein into the perforated tube (30), then the perforated tube, with the shutting means (49, 146) in a closed configuration, in such a way as to squeeze the material with drainage of its humid fraction through the holes in the perforated tube (30), and finally to continue its stroke into the perforated tube (30), with the shutting means (49, 146) in an open configuration, in such a way as to eject the squeezed material through the outlet end (30b) of the perforated tube.