A vehicle body speed estimating device. An attitude angle estimating mechanism estimates a roll angle and a pitch angle. A longitudinal speed computing mechanism computes longitudinal vehicle body speed. A vehicle body speed estimator estimates lateral vehicle body speed by using, as state amounts of vehicle motion, the longitudinal vehicle body speed and the lateral vehicle body speed, and on the basis of respective detected values of longitudinal acceleration, lateral acceleration and yaw angular velocity of vehicle motion, and respective estimated values of the roll angle and the pitch angle, and a product of a computed value of the longitudinal vehicle body speed and a value obtained from an absolute value of the detected value of the yaw angular velocity.