In rolling bearings, subsurface flaking failures occur under pure rolling contact fatigue conditions. In such failures, one of the crack initiation and its subsequent initial extention factors is believed to be the results of repetitive orthogonal shear stress. Accordingly, we have deemed that it is of critical importance to evaluate the shear fatigue properties, which can be obtained by torsional fatigue testing. However, up until now, it has been all but impossible to establish the shear fatigue properties of giga-cycle regimes because of conventional low loading frequency torsional fatigue testers. This is due primarily to time constraints. By contrast, ultrasonic fatigue testing is employed to assure high loading speeds. Ultrasonic tension-compression testers have been commercially available for more than a decade, and many data are being accumulated. However, there have been scant few investigations into ultrasonic torsional fatigue testing, and as such these limited to only a few low output-type converters of torsional vibration. With these considerations in mind, we have developed an ultrasonic torsional fatigue tester which enables for the rapid evaluation of shear fatigue properties. A loading frequency of 20 000 Hz is quite high, and as such results in a radical reduction of testing duration. It is possible to produce maximum shear stress amplitudes of about 950 MPa at the surface of specimen's minimum diameter. This is sufficient for the evaluation of high strength rolling bearing steels over wide ranges of loading cycles. For example, when loading cycles of 10¹⁰ are applied, the ultrasonic torsional fatigue tester requires only about seven days for complete testing, as compared with conventional testers at a loading frequency of about 10 Hz, would require more than 32 years.