The new practical use example of the JADER datasets from Japanese Adverse Drug Event Report database opened by Independent Administrative Agency Pharmaceuticals and Medical Devices Agency in April, 2012 and afterwards will be reported. The purpose of this study is to examine the evaluating method of medicine concomitant use risk by the frequency at which two or more medicines were reported simultaneously, being assumed the possibility of the influence of drug interactions to be the concomitant use risk in an adverse drug event onset. In order to estimate the potential degree of the safety risk at the time of the concomitant use, the methodology was estimated by the following procedures. 1) For considering that two suspicion medicine targeted is one medicine, the statistical signal index which means those of medicines with use in the case where they both are indicated in one report, the index of the concomitant use, is computed. 2) The statistical signal index about two target suspicion medicines is computed individually. 3) The case where the ratio of the index of the concomitant use to the index obtained individually exceeds 2 also in any of two suspicion medicines is judged as there being the concomitant use risk. The Proportional Reporting Ratio (PRR) and the Reporting Odds Ratio (ROR) were used as a statistical signal index. In order to check the validity of this method, Stevens-Jonson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) which are known for the adverse events of critical drug rash reported in JADER were taken up, and the causality of medical supplies limited to the medicine with which they were reported as a suspicion medicine. As for the combination of the suspicion medicine which fulfills the conditions of the concomitant use risk, 10 kinds of candidates out of 159 combinations for SJS and 22 kinds of candidates out of 111 combinations for TEN were detected, respectively. Although this approach for the concomitant use risk was considered to be an effective means in showing the above results, some issues about the ratio of the index of the concomitant use and criteria in the report numbers of the medicine to be chosen, the effective calculation method for combinations in more than 3 medicines, etc. will be required for the further examination.