To provide an inexpensive warning device for a crane, capable of easily warning a worker how close the crane approaches to a dangerous condition.

The warning device comprises dangerous condition detecting means for detecting how close the operated condition of the crane approaches to the dangerous condition, in accordance with a plurality of detection levels, and for outputting different signals and warning means for issuing a warning sound or a warning light which has shorter on-off cycles as the crane approaches closer to the dangerous condition, in accordance with the detection signals from the dangerous condition detecting means.