DETECTING INSTRUMENT OF POSTURE OF EXCAVATOR

PURPOSE:To enable the detection of a photodetecting position on biaxial directions with only a photodetector of uniaxial direction photodetecting position detecting type for simplification of the structure by using two pieces of photodetectors of uniaxial direction photodetecting position detection type arranged so that the mutual position detecting directions are right-angled and a half mirror freely rotating around an axial line. CONSTITUTION:A half mirror 4 is constituted freely rotatably around a datum axial line P' passing through its center so that a laser beam L1 reflected from the half mirror 4 may selectively be projected to the 1st and 2nd photodetectors 5A, 5B, and the photodetecting position of the reflected laser beam L1 in the direction of axis X and axis Y is detected respectively with 1st and 2nd photodetectors 5A, 5B by rotation switching operation of the half mirror 4. Consequently the constitution can be made with only two pieces of the photodetectors of photodetecting position detecting type in uniaxial direction that elements rows 9X, 9Y for one direction only are respectively placed in parallel in the 1st photodetector 5, and no lack of photodetecting element due to the crossing of mutual element rows is possible, and therefore the detection accuracy can be improved widely, also the structure is simplified.