| 摘要 |
PROBLEM TO BE SOLVED: To house a boom in a vehicle even in the case of a failure of a position sensor. SOLUTION: This boom operation controlling device 40 is provided with position sensors 41, 43, and 45 detecting a boom position, a sensor failure determining circuit 57 determining whether the position sensors 41, 43, and 45 are in failure or not, an operation restricting circuit 6 restricting operation of the boom in the direction, in which an overturning moment increasing working on the vehicle is increased, when the sensor failure determining circuit 57 determines that the position sensors 41, 43, and 45 are failed, and a contraction switch 49 detecting a full contraction state of a boom extension quantity. The operation restricting circuit 6 releases restriction on the boom lowering operation if it is detected that the boom is in a full contraction state by the contraction switch 49 when a failure of the position sensor is determined by means of the sensor failure determining circuit 57.
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