A surgical instrument, such as a surgical stapling instrument (1), comprises a tissue manipulating portion (2) which is intended to be introduced in the body of a patient, a handle portion (3) with an actuating mechanism (7) adapted to generate actuating movements for the actuation of the tissue manipulating portion (2) and comprising at least a pair of rotary output members (33 40) and an actuating transmission device (5, 5′ 6, 6′) connecting the actuating mechanism (7) of the handle portion (3) to the tissue manipulating portion (2) and comprising at least one pair of rotary rods (17, 17′ 19, 19′) for transmitting rotational actuating movements from the pair of rotary output members (33 40) to the tissue manipulating portion (2). The actuating mechanism (7) comprises synchronization means (31, 32, 32′ 38, 20 39, 39′) which link the movements of the two rotary output members (33 40) of the pair of rotary output members such that they counter-rotate at substantially the same speed.
