Primary percutaneous coronary interventions (PCI) have been developed to improve clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI). In primary PCI, the door-to-balloon time (DTBT) is closely associated with mortality and morbidity. The purpose of this study was to find determinants of short and long DTBT. From our hospital record, we included 214 STEMI patients, and divided into the short DTBT group (DTBT < 60 min, n = 60), the intermediate DTBT group (60 min ≤ DTBT ≤ 120 min, n = 121) and the long DTBT group (DTBT > 120 min, n = 33). In-hospital mortality was highest in the long DTBT group (24.2%), followed by the intermediate DTBT group (5.8%), and lowest in the short DTBT group (0%) (< 0.001). Transfers from local clinics or hospitals (OR 3.43, 95% CI 1.72–6.83, P < 0.001) were significantly associated with short DTBT, whereas Killip class 3 or 4 (vs. Killip class 1 or 2: OR 0.20, 95% CI 0.06–0.64, P = 0.007) was inversely associated with short DTBT in multivariate analysis. In conclusion, transfer from local clinics/hospitals was associated with short DTBT. Our results may suggest the current limitation of ambulance system, which does not include pre-hospital ECG system, in Japan. The development of pre-hospital ECG system would be needed for better management in STEMI.