Yuri Kumiai General Hospital is a community-based core hospital that treated approximately 14,000 patients in the emergency outpatient clinic in 2014, with approximately 7,800 walk-in patients on Saturdays, Sundays, and holidays. In April 2014, we incorporated an inhospital triage system for walk-in patients on weekends and holidays to quickly diagnose the conditions of patients in a crowded waiting room and promptly treat those requiring urgent care. Furthermore, in April 2015, we introduced the Japanese Triage and Acuity Scale (JTAS) to standardize the quality of triage care. Evaluation and analysis of 7,454 triage forms to identify future challenges revealed that the triage rate was 88% immediately after the incorporation of the JTAS, with 93 incomplete triage forms, 13 undertriage cases, and 18 overtriage cases. This showed that the severity of emergency was determined based only on subjective symptoms and complaints, with no application of objective physical assessment. We presented a list of analysis results to triage staff, further assessed undertriage cases, and provided feedback in monthly workshops. At 1 year after introduction, the rate of triage increased to 95%, with 12 incomplete forms, 9 undertriage cases, and 21 overtriage cases, and the number of cases increased where the severity of emergency was determined accurately from the entire clinical picture including vital signs and the cause of injury. These findings suggest that use of the JTAS enabled a standardized triage system to be established and that the assessment of undertriage cases and organization of continuous workshops improved the quality of triage and the skill of triage nurses.