PURPOSE: To increase drilling accuracy at the center of a reference mark by compensating a temperature drift (displacement amount) between the centers of an X-ray camera and a drill along time.

CONSTITUTION: From a difference between the center position of a reference mark 3A image before drilling taken by an X-ray camera 2 and the center position of a hole image after drilling, the displacement amount of the distance L between the center of the X-ray camera 2 and the center of a drill 26 is obtained along time as input data (in). Then a set value Ln is obtained by applying the input data (in) to the following equation to compensate the displacement amount due to temperature which is provided on the X-ray camera 2 and a servo mechanism 23 along time. Ln=K×Ln-1+(1-K)×(in) Where Ln is a set value after compensation, Ln-1 is a set value set one step before, (in) is an input data, and K is a coefficient (0<K<1).