Abstract: A safety device (1) for a fork lift truck (2) comprising a chassis (3), a front axle (4) and a rear axle (5) fitted with respective wheels (6, 7) and supporting the chassis (3), a lifting apparatus (8) attached to the chassis (3) at the front axle (4). The device (1) comprises means (31) for acquiring information relative to the load (X) lifted by the apparatus (8), a processing unit (18) connected to the acquisition means (31), and safety means (30) which act on the truck (2) following a signal (S, S1, S2) processed by the processing unit (18). The acquisition means (31) comprise a detector (50) attached to the lifting apparatus (8).