This study examined the possibility of applying the industrial accident insurance balance ratio to the calculation of the converted accident ratio in the credibility assessment of the PQ. Some correlations between the industrial accident insurance balance ratio and the converted accident ratio were found in the general tendency, however, there were no significant correlations between the two in the individual companies. Therefore, this study came to the conclusion that it is not appropriate to directly apply the industrial accident insurance balance ratio to the calculation of the converted accident ratio.