A motorized trimming apparatus having two blades placed side-by-side, has triangularly or trapezoidally cut teeth spaced apart from each other, at least one of said blades being movable to enable the cutting by shearing of wood inserted between said teeth, and connected to a drive device. The apparatus is characterized in that it comprises a means for controlling the drive device, said control means being constructed or configured so as to detect stops in movement of the movable blade(s) and to instantaneously and automatically control the reversal of the rotational direction of said drive device and thus control the reversal of the direction of movement of said movable blade(s).