PURPOSE: To facilitate quantification and high efficiency for an unloader to handle bulk material by detecting powder supplied to a longitudinal screw conveyer drive motor and controlling the speed of a travel and drive motor according to detected power.
CONSTITUTION: Electric power for a screw conveyer drive motor M 1 is fed from a power detection section 11 to a sequencer 10 in every fixed hours during unload operation. The sequencer 10 outputs a signal to instruct a travel speed, such as 10m/min. when the power is less than 200kw and 8m/min. when 200kw or more and less than 250kw, according to the power to a travel control section 12. The travel control section 12 outputs a control signal to a voltage control section 13 in accordance with such instruction to control the speed of a travel and drive motor M 2 . In this way, it is possible to perform unload work of quantification and high efficiency, independent of a bulk condition and driving performance.