PURPOSE: To observe visually a clearance between the bottom surface of a bucket and the ground surface easily by an operator, by fixing guide plates to the bottom surface of the bucket, and projecting the rear ends of the guide plates to the rear side of the bucket.

CONSTITUTION: Guide plates 38 and 39 are fixed to the bottom surface 11b of a bucket 11 at the positions of ribs 31, 32, and 34. Then, the rear ends of the guide plates 38 and 39 are projected to the rear side of the bucket 11. And the guide plates 38 and 39 are made possible to be observed visually by an operator at the operator seat 14. Furthermore, the rear surface 11c of the bucket 11 is curved so as to glasp a clearance between the bottom surface 11b of the bucket 11 and the ground surface very easily. Consequently, the position regulation of the bucket 11 can be carried out simply, and the working efficiency can be improved without requiring a highly skillful techincs.