| 摘要 |
PROBLEM TO BE SOLVED: To prevent a bench from swinging suddenly during derricking motion of a boom, with a simple structure. SOLUTION: A controller 7 is constituted of an inclination angle detecting means 8 detecting the inclination of a bench, a boom hoisting driving condition detecting means 10 detecting if a boom is subjected to derricking drive, and a control signal output part 9 generating and outputting a control signal for driving a leveling actuator necessary to cancel an deviation between a detected inclination angle from the inclination angle detecting means and a target angle for storage. The signal from the boom hoisting driving condition detecting means is inputted in a control signal output part, and a control signal output part is formed so as to update the target angle stored in, into the inclination angle from the inclination angle detecting means and store it at the time of starting boom hoisting driving.
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