To provide a oblique contact double ball bearing and a pre-load adding method for the ball bearing capable of easily adding the pre-load by performing adjustment for adding the pre-load in a wide adjustment range. In this oblique contact double ball bearing, clearances between balls and raceways and on one row are made different from clearances between balls and raceways on the other row so as to apply a thrust load to inner and outer rings, and add the pre-load to the inner and outer rings.