PURPOSE: To improve workability by detecting the position of a bucket by using an automatic tracking type position measuring device and various detectors while conducting excavation as monitoring the display of the positional coordinates by an operator.

CONSTITUTION: An automatic tracking type position measuring device 3 installed on the ground automatically tracks an antenna 2 mounted to a backhoe 1, and transmits the positions of the coordinates over the backhoe 1. The strokes of each cylinder of a boom 1A, an arm 1B and a bucket 1C are detected by the backhoe 1 while the relative positions of the front end section of the bucket 1C and the antenna 2 are computed from values detected by a gyro compass 8, a pinching meter 9 and a rolling meter 10, and converted into coordinates, where the position of the antenna 2 is used as an origin. The coordinates are corrected by the coordinates of the antenna, and the coordinates of the front end section of the bucket 1 are obtained, and displayed onto a display 13. Accordingly, since the backhoe can be positioned easily, the backhoe can be carried out accurately even by an unskilled person, labor can be saved, and the cost of execution can be reduced.