an internal operation unit having a lever which operates boom length and angle and swing angle in a crane and for outputting the operation of level as an electrical signal; an internal and external select unit connected to the internal operation unit, the crane and a moment limiter, for supplying data on the boom length and load to the moment limiter; an internal output display unit connected to the internal and external select unit, for displaying an imitation signal outputted from the crane during a room operation; a drive circuit connected to the internal and external select unit, for amplifying the output signal from the internal and external select unit over a predetermined level; and a sensor and crane state display unit connected to the drive circuit, for displaying a signal value outputted from the internal and external select unit and displaying the boom length and angle corresponding to the signal value.
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