Manually operated instrument (1) for filling syringes (3) having a plunger (5) provided with a seat (7) for a shaft controlling sliding of said plunger within the barrel (11) of the syringe, said instrument being equipped with coupling means (13a) for coupling to said seat (7) of the plunger (5), wherein said coupling means are firmly attached to one of the ends of an externally threaded shaft (9), and wherein the instrument comprises an actuating grip nut (15) provided with an internally threaded through-hole (17) through and with which said threaded shaft (9) passes and comes into engagement.
