Inclusion Criteria:  Age ≥ 19 years old  Non-ST-segment elevation myocardial infarction  Angina pectoris or equivalent ischemic chest discomfort with at least 1 of 3 features and,  occurs at rest, usually lasting > 10 minutes severe and new onset (within the prior 4-6 weeks) crescendo pattern  Elevated cardiac biomarkers and,  ≥ 99% value of high-sensitivity cardiac troponin No ST-segment elevation ≥ 0.1 mV in ≥ 2 contiguous leads or newly developed left bundle branch block on 12-lead electrocardiogram PCI within 72 hours after symptom development Multivessel disease: Non-IRA with at least 2.5 mm diameter and 50% diameter stenosis by visual estimation Patient's or protector's agreement about study design and the risk of PCI  Exclusion Criteria:  Cardiogenic shock at initial presentation or after treatment of IRA TIMI flow at non-IRA ≤ 2 Severe procedural complications (e.g. persistent no-reflow phenomenon, coronary artery perforation) which restricts study enrollment by operators' decision Non-IRA lesion not suitable for PCI treatment by operators' decision Chronic total occlusion at non-IRA History of anaphylaxis to contrast agent Pregnancy and lactation Life expectancy < 1-year Severe valvular disease History of CABG, or planned CABG Fibrinolysis before admission