The invention relates to an improved-structure instrument (1) for allowing the alignment of fixing screws (2) to be inserted in transverse holes (3, 13) of nails (4) for long bones, in particular medullary nails, of the type comprising an arched arm (15) having a free distal end (6) connectable to a proximal end (16) of a head (7) of the nail (4) in which the transverse holes (3, 13) are formed, and a proximal handle portion (5), as well as a connection portion (20) between the distal end (6) and the proximal handle portion (5). Advantageously, the connection portion (2) comprises at least one through-hole (23, 33) for receiving a guide tube (10) for a drilling bit, the through-hole (22, 33) having an axis coinciding with the axis of one of the transverse holes (3, 13,) and manually operated quick-locking means (25) are associated with the through-hole (23, 33) so as to lock in a stable position the corresponding tube (10) inserted in the instrument (1).
