The overhanging storage mechanism for a jib is provided with: a guide roller (31) provided to a jib (15); a guide (32) provided to a base end boom (14a); a jib-fixing pin (43) provided to the base end boom (14a); and a pin socket (45) that is provided to the jib (15) and that comprises insertion holes (48), (49). The jib-fixing pin (43) and the insertion holes (48), (49) are arranged so that the jib-fixing pin (43) is inserted in the insertion hole (48) when the jib (15) moves along the base end boom (14a) together with contraction of a boom (14). The inner dimensions of a front end opening (48) are larger than the outer dimensions of the jib-fixing pin (43). It is thus possible to absorb positional displacement between the jib-fixing pin (43) and the insertion hole (48).