For the optimal design of ball bearings, measurement and its elucidation of complex three-dimensional ball motion are very essential. Only the way to detect ball motion in a ball bearing is the magnetic measuring method, developed by Kawakita et al.. However, due to the considerable effect of errors in the measurement, the angular velocity components of ball rotation analyzed by their method lead to problems on the accuracy in analyzing the contact angle and spin moment of the ball. In this report, by applying the magnetic measuring method to the ball bearing under the axial load, the main causes of error affecting the detection output were clarified. Also, using frequency analysis, a simplified method was proposed to analyze the angular velocity components of the ball rotation. Finally, evaluation and examination were carried out about the practicality of our method.