This paper describes a new automatic method for detecting defects in ball bearings. The detection of defects is currently carried out by inspectors who listen to vibration signals obtained by a vibration pick-up in the Anderon meter. The pick-up is attached to the outer ring of a ball bearing while the inner ring rotates at a uniform speed. Several methods have been proposed so far for the automatic detection of flaws. These methods are based on the periodicity of vibration pulses excited by flaws. However, the periodicity of vibrations is not always guaranteed when (a) there are slight flaws on the surface of the race, (b) there are flaws on the surface of balls, and (c) there is dust in the grease. However, we have developed a new method, by which the non-periodic resonant vibrations due to both slight flaws and dust are detected. We have applied this new method to the detection of these defects in small-sized ball bearings; the defects were detected with an 98 % accuracy rate.