Recently, a demand of miniaturization and performance enhancement of the printed wiring board is intensified more and more with the rapid popularization of the information terminal electronic equipment. The processing by the micro drill is generally used in small diameter drilling of the printed wiring board made of GFRP. Then, the through-holes of small diameter are desired for the miniaturization of the equipment. There is an internal damage of micro drilled hole in one of the problems in the formation of the through-hole in the micro drilling. The purpose of this report is to apply a data mining method (that is the method of statistically analyzing the factors) to the image processing data of micro drilled holes, and to elucidate the factors which influences internal damage generalizing. Following conclusions were obtained : (1) It is clear that the internal damage depends on three factors (the thickness of fiber bundle drilling hole wall side, the feed rate and the width of reverse fiber bundle). (2) We can indicate a practical formula to predict the internal damage width around the micro drilled hole by a data mining method.