A locking/unlocking device (1) is described for a blade clutch lever (2) particularly for a lawnmower, said lawnmower comprising a frame (3), a chair-seat (4) selectively positionable between a loaded chair-seat position and an unloaded chair-seat position, said clutch lever (2) selectively movable in a seat (5), integral with the frame (3), between a first position of clutched blade and a second position of unclutched blade, Said device (1) comprises a hook-like element (6) for directly locking the clutch lever (2), which is selectively movable between a first engagement position and a second disengagement position of the clutch lever (2), control means (7, 8) associated with the hook-like element (6) to place it in the engagement position of the clutch lever (2), the operation of said control means (7, 8) being associated with the positioning of the chair-seat (4), and contrast means (9) of the control means (7, 8) to position the hook-like element (6) in the second disengagement position of the clutch lever (2). (Fig. 6).
