This study aimed at clarifying the issues of the system that needs to be improved in order to raise the precision of computer-assisted ICD-10 encoding, by analyzing the inconsistency between the codes registered by physician and encoded by experts in discharge summaries of the electronic patient record system. It was found that human related factors led to the major inconsistency at the chapter level of ICD-10. Substantial commitment of coding experts was considered practically important to correct careless mistakes in physician's entry and assign accurate codes to complicated diagnoses, while relatively small improvement of the system was thought feasible as countermeasures against the inconsistency caused by system related factors.