A bearing device for a wheel, where preload control is easy and a uniform amount of preload can be applied even if a bearing seal is installed in the bearing device. The bearing device rotatably supports a wheel and has an outer member 1, an inner member 2, and rolling elements 3 interposed between both members. The outer member 1 has on its outer periphery a vehicle body installation flange 1a, and double row rolling surfaces 6, 7 are formed on the inner peripheries of the outer member. Rolling surfaces 8, 9 facing the rolling surfaces 6, 7 of the outer member 1 are formed in the inner member 2. Between the rolling surfaces of both members 1, 2 are interposed the rolling elements 3. A sensor 4 for detecting the amount of preload of the bearing is provided on either the outer member 1 or the inner member 2.