An extend-retract system that enables the compact structure capable of horizontally extending with three segments that enables the outriggers to be extended and retracted by means of a single piston by opening and closing telescopically in a synchronous manner in telescopic boom or knuckle boom cranes, comprising - a main sleeve rail with a fixed structure, - a 1 st rail that is configured to open and close by moving back and forth within the main sleeve rail , - a 2 nd rail that is configured to open and close by moving back and forth within the 1 st rail , - a 3 rd rail that is configured to open and close by moving back and forth within the 2 nd rail , - a piston sleeve with a fixed structure connected into the 2 nd rail , - a 1 st rod , which is engaged into the main sleeve rail and which is configured to open and close the 1 st rail by entering into the piston sleeve , - a 2 nd rod , which is engaged into the 1 st rail and which is configured to enter into the piston sleeve to open and close the 2 nd rail - a 2 nd pulley (120 - an extending chain or rope that is configured to open the 3 rd rail by extending the same on the 2 nd pulley engaged to the 3 rd rail , - a 1 st pulley , - a retracting chain or rope that opens the 3 rd rail by retracting the same on the 1 st pulley engaged to the 2 nd rail , - a rail , - an organized chain which is configured to moveed back and forth within the rail connected to the 1 st rail , - a hydraulic line that is configured to move within the organized chain and enable the movement of the 1 st rod and 2 nd rod , - an electric line that is configured to move within the organized chain with the hydraulic line and that is configured to provide the electrical connections of the outrigger, - a pipe that conveys the hydraulic line and electric line to the end of the 3 rd rail . - a main sleeve rail with a fixed structure, - a 1 st rail that is configured to open and close by moving back and forth within the main sleeve rail , - a 2 nd rail that is configured to open and close by moving back and forth within the 1 st rail , - a 3 rd rail that is configured to open and close by moving back and forth within the 2 nd rail , - a piston sleeve with a fixed structure connected into the 2 nd rail , - a 1 st rod , which is engaged into the main sleeve rail and which is configured to open and close the 1 st rail by entering into the piston sleeve , - a 2 nd rod , which is engaged into the 1 st rail and which is configured to enter into the piston sleeve to open and close the 2 nd rail - a 2 nd pulley (120 - an extending chain or rope that is configured to open the 3 rd rail by extending the same on the 2 nd pulley engaged to the 3 rd rail , - a 1 st pulley , - a retracting chain or rope that opens the 3 rd rail by retracting the same on the 1 st pulley engaged to the 2 nd rail , - a rail , - an organized chain which is configured to moveed back and forth within the rail connected to the 1 st rail , - a hydraulic line that is configured to move within the organized chain and enable the movement of the 1 st rod and 2 nd rod , - an electric line that is configured to move within the organized chain with the hydraulic line and that is configured to provide the electrical connections of the outrigger, - a pipe that conveys the hydraulic line and electric line to the end of the 3 rd rail . <EOS>