The invention relates to a passing device for optical fiber systems, resistant to pressure differences, which allows the transmission of an optical signal, by means of an optical fiber, between two enclosures inside which the gas or liquid pressure is different, or towards the interior of an enclosure inside which the gas or liquid pressure is different from the outside pressure. According to the invention, the device consists of a metal sleeve () with an inside diameter that allows the introduction of any type of connector (), which is fastened into the wall of an enclosure () or into the partition wall of some enclosures (), inside the sleeve () there is mounted an O-ring joint () used for sealing in relation to the metal sleeve () another metal box () which has mounted, in its lower part, two reducing washers () whereon there is placed an elastic silicone adhesive () limited by other two reducing washers (), the entire metal box () being pressed on the O-ring joint () by a nut (), so that the assembly consisting of the nut (), the reducing washers (), the metal box (), the O-ring joint () and the metal sleeve () provides the tightness of the space between the optical fiber () which crosses them all, the metal box () and the metal sleeve ().