To provide a boom structure capable of facilitating work for arranging a line-shaped member to a boom lower face by preventing decline in strength by a relatively simple structure.

The boom structure includes a traveling body 10; a hollow longitudinal boom 30 provided in the traveling body 10 at least to enable derricking motion and having an inner space extended in the longitudinal direction; a cylinder bracket 70 provided on the lower face of the boom 30; and a derricking cylinder 24 having one end pivotally connected to the cylinder bracket 70 to derrick the boom 30 and the other end pivotally connected to the traveling body 10. The boom 30 includes an outlet 34 formed on the lower face of the boom 30 and communicated with the inner space and the line-shaped member 40 extended inside the inner space and drawn out and wound from the outlet 34. The outlet 34 is positioned between a tip member 72 of the cylinder bracket 70 and an erected plate member 73 in the boom longitudinal direction in the vicinity of the mounting position of the cylinder bracket 70.