In a wheel supporting rolling bearing unit in which pitch circle diameters of balls 6a, 6b in an outside row and an inside row are made different, contact angles αOUT, αIN of the balls 6a, 6b in the two rows in a completed state are equal to each other. Initial contact angles βOUT, βIN of the two rows are smaller than predetermined contact angles αOUT, αIN. The extent [αIN−βIN] to which the initial contact angle βIN of the balls 6b, 6b in the inside row is made smaller than the predetermined contact angle αIN of the balls 6b, 6b is made larger than the extent [αOUT−βOUT] to which the initial contact angle βOUT of the balls 6a, 6a in the outside row is made smaller than the predetermined contact angle αOUT of the balls 6a, 6a {[αIN−βIN]>[αOUT−βOUT]}. By this configuration, imparting the predetermined contact angles αOUT, αIN to the balls 6a, 6b in the two rows in the completed state, and the preloads and contact angles of the balls 6a, 6b in the two rows are made proper.