There are many researches on the noise of the ball bearing, and their conclusions about noise source can be divided into two main opinions ; one is due to the elastic vibrations of the outer ring, the other is the vibrations of the cage or ball. However, these conclusions are only based on a hypotheses. So, first, the auther measured the noise of three kinds of the simple single raw deep groove ball bearings, analyzed about the peak value of the frequency spectrum, and obtained the results as follows : - 1) The noise of a simple ball bearing is due to the vibrations of the outer ring. 2) In the above vibrations, there are radial and axial bending ones, and they have the first and second modes respectively. 3) On the axial load, another vibration exists and its vibratory system which was found by Mr. Tanaka, consists of the mass of the outer ring and the stiffness of the ball bearing for axial direction.