A device that can stably and accurately estimate the roll angle of a vehicle body during various states of movement of the vehicle body. A roll angle estimated value calculation portion calculates an estimated value of the roll angle by integrating a value obtained by correcting an estimated value of roll angle velocity of a vehicle body by use of a correction value, or by correcting a value obtained by integrating an estimated value of roll angle velocity by use of a correction value. The correction value is calculated by use of a detection value of speed of the vehicle body in the traveling direction, detection values of angular velocity and acceleration detected by sensors mounted on the vehicle body, a previous estimated value of the roll angle, and a previous estimated value of the pitch angle of the vehicle body.