An eddy current flaw detection sensor is provided which can detect a circumferential crack occurring at the deformed portion or peripheral portion thereof of a heat transfer tube with a high degree of sensitivity. Two excitation coils 1a, 1b cause eddy current B to flow in the axial direction of a tubular test object 31. A detection coil 2 disposed between the excitation coils 1a, 1b detects bypass eddy current D which flows in the circumferential direction of the test object 31 while bypassing a circumferential crack E. For this purpose, the coil axes of the excitation coils 1a, 1b are directed to the radial direction of the cylindrical protection member 3 and the coil axis of the detection coil 2 is directed to the axial direction of the protection member 3.