An apparatus for operating a boom of a crane is provided to reduce abrasion of a packing member frictionized with first and second inner booms by reducing the drawing and insertion time. An apparatus for operating a boom(20) of a crane draws and inserts first and second inner booms(24,26) inserted into an outer boom(22). A hydraulic cylinder(25) includes a rod(25a) connected to the outer boom and a pin(28) and a cylinder unit(25b) connected to the first inner boom and a pin(30). First and second sprockets(34,36) are installed both ends of the first inner boom, respectively. One end(38a) of a first chain(38) is connected the outer boom and the other end(38b) of the chain is connected to one side of a bracket(27). One end(40a) of a second chain(40) is connected to the outer boom and the other end(40b) of the chain is connected to the other side of the bracket. The first inner boom is drawn and inserted from the outer boom according to the cylinder unit operation of the hydraulic cylinder. The second inner boom is drawn and inserted together with the first inner boom by pulling force of the first chain according to the drawing operation of the first inner boom and by the pulling force of the second chain pulled according to the insertion operation of the first inner boom.
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