In an effort to improve the safety of surgery, we investigated the incidents related to surgery using a laser or an electric scalpel, not to mention other equipment. The subjects included in this study were 86 cases who experienced incidents related to their surgery that we found in the reports of the Japan Council for Quality Health Care. We searched for a breakdown of the medical equipment used and the influence on the patient, and analyzed the causes of the incidents to determine whether new recommendations might reduce the risk of incidents. The breakdown of the medical equipment included 61 electric scalpels, 11 light sources, 7 radio wave cautery devices, 5 lasers, and 2 supersonic wave coagulation incision devices. The incidents were 46 burns, including 18 with no adverse outcomes, 8 cases with a foreign body left after surgery, 6 cases of damage to a proximal organ, 3 cases with perforations and 5 other incidents. The causes were 33 errors in the use of the equipment, 20 malfunctions and/or damage to the equipment, 17 cases of sudden ignition, 9 cases in conjunction with the use of a counter electrode plate, and 7 other causes. Many incidents were related to the use of a heat source apparatus, such as an electric scalpel or laser. Because most incidents were due to a lack of knowledge and recognition, taking countermeasures including increased education may be able to prevent the majority of incidents. Medical workers can reduce incidents by recognizing the risks, increasing their knowledge about the devices and sharing countermeasures as a team. (J. Jpn. Soc. Laser Dent. 25:136 ~ 139, 2014 Reprint requests to Dr. SUZUKI) Key words= Laser, Electric scalpel, Incident キーワード=レーザー,電気メス,インシデント