PURPOSE: To secure and facilitate a hole searching method by detecting a contact force between a bar-like part and a hole-having surface while scanning on said surface in an inclined direction, defining the initial part at which a detected value has changed by more than a certain amount, as a front edge while the next part as a rear edge, repeating the detection in a different direction and obtaining a total average.

CONSTITUTION: In a first scanning, a hand 1 holding a bar-like part 2 is inclined at an angle θto an inserting direction to carry out scanning in a direction 10 on a surface 4 having a hole 3 for inserting the bar-like part 2 while pressing the hand 1 in the inserting direction, and a force applied to the hand 1 is detected and recorded. Then, in a second scanning, the pressing is released and the hand 1 is returned to a starting point to carry out scanning in a different direction 11. Thus, a scanning over a zone including an inserting hole 3 can be carried out by repeating the first and second scanning. In the first scanning, when the bar-like part 2 is in contact with the face 4, a reaction FV is applied in the direction perpendicular to the surface 4, no force is detected while the bar-like part is traveling in the inserting hole 3 and, at the point of time when the bar-like part 2 is again brought into contact with the surface 4 out of the inside of the hole, a reaction FH is applied in the direction parallel to the surface 4. By obtaining the average of these coordinates, the central coordinate of the hole 3 can be obtained accurately and rapidly.