PURPOSE: To economically increase live load capacity by articularly connecting a second main jib supported on a platform, to a first main jib through bearing structure disposed almost horizontally.

CONSTITUTION: An upper frame 2 rotatably disposed on a lower frame 1 of a crane has a first main jib 3 formed to be lightweight. In addition to a live load capacity increasing device such as a super lifting device 7, a second main jib 8 supported to a platform 10 is articularly connected to the main jib 3 through bearing structure 30 disposed almost horizontally. The bearing structure 30 is formed of a derricking jib 4 used as a compressive force resistant member and held by a bar or a rope 11 with a horizontal member 12 fixed thereto. A set of rollers 12a, 12b for pulleys 13, 15 are supported in the horizontal member 12, and the crane side pulley 13 is connected to ropes 14a, 14b from a hoisting machine 2. The pulley 15 is connected to ropes 16a, 16b from a hoisting machine of the platform 10.