There is a need for improving the accuracy of estimating a gain error for an angular velocity sensor. An error estimation section and a correction section are provided as well as a gyroscope that detects an angular velocity of a vehicle. The error estimation section assumes the gain error of the gyroscope to be a state quantity and finds an estimated value for the gain error using a Kalman filter. Based on the gain error found by the error estimation section, the correction section corrects a gain correction amount used for gain correction of values detected by the gyroscope. The correction section corrects the gain correction amount dedicated to right turn based on the gain error found by the error estimation section when the vehicle is assumed to turn right. The correction section corrects the gain correction amount dedicated to left turn based on the gain error found by the error estimation section when the vehicle is assumed to turn left.