| 摘要 |
PROBLEM TO BE SOLVED: To dissolve the problems that a work machine is excessively lowered and the hard plate of a field is damaged when a work machine is lowered next because laser beams can not be caught since mud is stuck to a light receiving device, light reception is obstructed since an automobile or the like travels near the field or erroneous laser beams are received by reflected light at the time of elevating the work machine when the light emitting device of lasers is erected on the ridge part of the field, the light receiving device for receiving the laser beams is provided on a tractor side and cultivation control is performed with the irradiation surface of the laser beams as a reference. SOLUTION: In this work machine elevating/lowering device 27 of a tractor, the work position of the work machine 5 is stored by a lift arm angle A before the elevation at the time of elevating the work machine 5 and the lift arm angle A before the elevation is turned to the reference and a limit is provided on the position of an angle (A-α) by it at the time of lowering the work machine 5 next.
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