To provide a guide hole boring device which can always precisely bore a guide hole in a printed board without being affected by ambient temperature.

In a table 2 on which the printed board 10 is mounted, a side plate 14 made of a material having a very small coefficient of thermal expansion is buried and arranged. When the guide hole is bored, images of reference position marks 15a and 15b formed on the subplate 14 are picked up by X-ray image pickup devices 4a and 4b are processed to compute the distance between the two reference position marks 15a and 15b. The distance between the two reference position marks 15a and 15b is predetermined, so the boring position of the guide hole is corrected according to the error based upon the computed distance. Through this operation, the guide hole can be bored always with high precision irrelevantly to variation in the ambient temperature.