JIB CONNECTION STRUCTURE

Provided is a jib connection structure that is capable of connecting a jib base end engagement part and a jib connection shaft even when a boom undergoes natural extension, and that is capable of restraining a jib from swinging sideways in a state where the jib is projected. This jib connection structure comprises: jib connection shafts (21, 22) projecting horizontally toward both sides from a boom tip end part (14a); and jib base end engagement parts (31, 32) respectively provided to bifurcated jib base end parts (15a). Each jib base end engagement part (31, 32) is U-shaped into which the jib connection shaft (21, 22) can be fitted, and is provided with an insertion hole (31h, 32h) into which a pin (33, 34) for preventing the jib connection shaft (21, 22) from slipping out is inserted. The insertion hole (32h) in one jib base end engagement part (32) is arranged more toward the outside than a U-shaped bottom part (32b). When the jib base end engagement part (32) and the jib connection shaft (22) are connected, a gap (d1 is formed between the pin (34) and the jib connection shaft (22). When a jib (14) is projected, the gap (d2) between the pin (34) and the jib connection shaft (22) becomes smaller.