| 摘要 |
PROBLEM TO BE SOLVED: To facilitate driving operations by automatically controlling a pushing force imparted by a lifting device to excavating device. SOLUTION: The excavating device 8 is connected to the lower portion of an upper frame 5 provided on a leader 1, in such a manner that the interval between the excavating device and the lower portion is variable. When a pressure generated in a cylinder 11 provided between them reaches a set upper limit pushing force f1 because of a decrease in the interval between them as the descending speed of the upper frame 5 becomes faster than the descending speed of the excavating device 8, the lowering of the upper frame 5 is stopped; when the pressure of the cylinder 11 is equal to or less than a set lower limit pushing force f2, the upper frame 5 is lowered.
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