A spindle direction engaging device moves at least one of spindles in a mutually separating direction to closely engage a lock piece or a lock portion in a spindle direction of spindles while the lock piece is locked to the lock portion when a tire is not mounted. A second spindle includes a groove extending in a peripheral direction along an outer periphery thereof in sliding contact with the lock piece; sliding surfaces of the lock piece and the groove are receiving portions formed as flat surfaces to receive separating forces acting on both the spindles. A correction device corrects a gap between an inner ring of the spindle bearing and rolling elements of the spindle bearing, or a gap between an outer ring of the spindle bearing and the rolling elements of the spindle bearing, while the spindle is rotating. Preload bolts include a coolant passage formed by hollowing a corresponding portion passing a mounting hole of a detector, and a coolant can thus be supplied to the coolant passage.