It is well known by experience that a noise of simple ball bearing is affected by the clearance. However, there has been no research work which described clearance effect on simple ball bearing noise and its causes. The author measured the noise of simple ball bearing with known radial clearance, analyzed about the peak values of the frequency spectrums, and obtained the results as follows : - (1) The noise of a simple ball bearing is affected by the amount of radial clearance, loading direction and the amount of load etc. (2) The frequencies and the total sound pressure level of the noise are increased by decreasing radial clearance. (3) Principal frequencies of the noise correspond to the bending natural frequencies of the outer ring with load. (4) The total sound pressure level of the noise is determined by the sound pressure level of a peak in the case of axial load, but the sound pressure levels of all peaks in the case of radial load.