A synchronising device (2) is disclosed for interconnecting and transmitting a torque between two rotary elements of a shift gear box, in particular for connecting a transmission shaft (4) to a gear wheel (6, 8) mounted to rotate on the transmission shaft (4). A synchroniser sleeve (30) has an outer disk carrier (36) connected to a shift gear element (64) and an inner disk carrier (34). A set of disks (40) is provided between the disk carriers (34, 36). The adjacent disks of the set of disks (40) are alternately connected to the inner disk carrier (34) or to the outer disk carrier (36). When the speed of rotation of the outer disk carrier (36) differs from that of the inner disk carrier (34), the disks allow a synchronisation moment to be achieved. For that purpose, the outer disk carrier (36) has a device (62) for form-fittingly locking the outer disk carrier (36) to a device (60, 76) at the gear wheel (6, 8). After the outer disk carrier (36) moves axially in the direction of the gear wheel (6, 8) to be connected, form locking is achieved before the torque-transmitting coupling teeth (24, 26, 32) between the inner disk carrier (34) and the gear wheel (6, 8) engage each other. The inner disk carrier (34) is permanently secured in rotation to the transmission shaft (4) and a spring element (42) is capable of constantly exerting a force on the set of disks (40) to achieve a synchronisation moment. The friction disks preferably have paper linings. The form locking devices and the coupling teeth may be spring-mounted and have stub ends.