A 77-year-old man, who underwent PCI 11 times in all three branches for unstable angina pectoris and who was taking SGLT2 inhibitor for diabetes mellitus, visited our emergency department because he felt chest strangulation when walking uphill. A 12-lead ECG showed a new ST elevation of more than 0.1 mV at V3~5, and transthoracic echocardiography showed mild hypokinesis in the intermediate posterior wall. Blood tests showed 448 pg/ml of NT-proBNP and that troponin T was slightly elevated at 0.056 mg/ml, leading to a diagnosis of non-ST-segment elevation acute myocardial infarction. The patient was urgently admitted to the hospital with a plan to perform PCI within 24 hours of arrival. After admission, he was prohibited from food intake and started on continuous saline infusion. On the second day, CAG was performed, and 90% stenosis was found in the left coronary artery Seg. 13. During PCI at the same site, the patient went into shock vitals, with urinary ketones 4+ and metabolic acidosis, and was diagnosed with euglycemic diabetic ketoacidosis (EDKA). The acid–base balance was normalized by continuous intravenous small-dose insulin infusion and glucose loading, and the administration of hypertensive drug was terminated on the fifth day of the disease. SGLT2 inhibitors are known to be cardioprotective and renal-protective, and are currently used in many patients. Three days prior to surgery for the withdrawal of SGLT2 inhibitors is recommended, but it is difficult to ensure a sufficient withdrawal period in emergency surgery. There are few case reports of EDKA occurring in this manner, and we report this case with a discussion of the literature.