A correction circuit stores data for obtaining coefficients of a relational expression indicating a relationship between a disturbance magnetic flux and a rotational angle error. Then, the coefficients are obtained from the data for obtaining the coefficients, and a detection result of a magnetic sensor is corrected based on the coefficients obtained, a relational expression, and a detection result of a disturbance magnetic flux detection circuit. Since it is possible to obtain the rotational angle error with respect to the disturbance magnetic flux from the coefficient obtained and the relational expression, it is not necessary to store the data indicating the relationship between the disturbance magnetic flux and the rotational angle error for all of the disturbance magnetic flux value in disturbance magnetic flux regions that may be applied.