To prevent an outer boom from abutting on a height limitation object, in any attitude of a folding crane having two booms, that is to say, an inner boom and the outer boom.
A height limitation device includes: a first angle detector which detects a ground inclination angle of an inner boom; a second angle detector which detects a ground inclination angle of an outer boom; a boom length detector which detects the length of the outer boom; and a height limitation part which controls a crane on the basis of detection information of the three detectors. The height limitation part monitors heights of four parts, that is to say, an upper part of a leading end of the outer boom, an upper part of a back end of the same, and upper and lower parts of a back end of a second outer boom, and regulates output of an alarm or movement of the outer boom to the side of its limit height when the height of any one of the monitored parts exceeds a predetermined height lower than the limit height.
Megumi Konishi
Hide Tanaka Tetsu
Ichi Hirose