one second displaceable running carriage which however cannot be seen in the illustrated figures the running carriages have rolling bodies for transmitting the load of the drawer 3 a synchronization device according to the invention makes it possible to prevent incorrect movements of the rails 6 7 and or incorrect movements of a running carriage mounted displaceably between the rails 5 6 7 fig2 shows a cross section of the extension guide 4 wherein the carcass rail 5 to be fixed to the furniture carcass 2 the central rail 6 which is displaceable relative to the carcass rail 5 and the drawer rail 7 to be connected to the drawer 3 can be seen here mounted displaceably between the carcass rail 5 and the central rail 6 is at least a first running carriage 8 which embraces a horizontal limb of the carcass rail 5 at least one second running carriage 9 is mounted displaceably between the central rail 6 and the drawer rail 7 the first running carriage 8 has rolling bodies 8 a 8 b and the second running carriage 9 has at least one rolling body 9 a for transmitting the load of the drawer 3 to avoid incorrect movements of the rails 5 6 7 and or the running carriages 8 9 the extension guide 4 has a synchronization device 10 with a synchronization wheel 11 which synchronizes at least one of the movable rails 6 7 with at least one of the two carriages 8 9 in the illustrated embodiment a relative movement between the first lower running carriage 8 and the drawer rail 7 is synchronized in the illustrated configuration it is also possible that the upper running carriage 9 can remain.