Very high cycle fatigue is mainly characterized by sub-surface fracture in the long regime over 10^7-10^8 cycles. However, since the detection of internal cracks is extremely difficult, the mechanism of very high cycle fatigue has not been clarified yet. In recent researches, small internal inclusions in steel were detected by using synchrotron radiation μCT imaging in the Super Photon ring-8 GeV (SPring-8). These results suggest a possibility that small cracks initiating inside metal material are observable. Focusing on the possibility, the present work conducted non-destructive observations of internal cracks by using the X-rays μ CT imaging in SPring-8 on Ti-6Al-4V alloy m which fatigue damage was accumulated. In order to open the internal crack during observations, a tensile load was given to the specimen. As a result of the series of observations, small internal fatigue cracks with a size of about 30 μm were successfully detected under the optimum tensile load necessary to open and identify those cracks. In addition, it was revealed that multi-cracks initiated inside the specimen and the fatigue life was determined by the competition of those propagations. The results obtained in this study showed that non-destructive inspection technique to detect small internal fatigue cracks was established.