An ultrasonic testing technique was studied for a hollow axle with a 30 mm bore diameter manufactured on a trial basis for conventional railway vehicles. To compensate for the decrease in crack detection sensitivity due to the small bore diameter, a piezocomposite focal probe was designed. It has been demonstrated that the ultrasonic testing equipment thus developed could detect artificial flaws with a depth of 0.15 mm at the non-fitted central part and those with a depth of 0.3 mm at the inner end of the wheelseat (fitted part). The accuracy of axle inspection for conventional railway vehicles equipped with such hollow axles will match that of Shinkansen vehicles.