The authors have performed micro computed tomography(μCT) with synchrotron radiation of SPring-8 to evaluate the fatigue crack propagation behavior inside specimens. A compact biaxial rotating bending fatigue testing machine was developed to make fatigue testing in SPring-8. Preparatory experiments demonstrated that the resulting data by the machine developed were consistent with the data by conventional Ono-type rotating bending fatigue testing machines. Fatigue crack propagation curves and da/dN-ΔK relation obtained by μCT corresponded to the data with replication technique on the surface of the specimens, however, it was also shown that the replication technique would not always present relevant information on the crack behavior.