an input configured to sequentially input magnetic data that is output from a magnetic sensor, said magnetic data being two-dimensional vector data that is a linear combination of a set of first fundamental vectors;

memory configured to store a plurality of the magnetic data as a data set of statistical population in order to update an old offset of the magnetic data with a new offset; and

an offset derivation module configured to calculate the new offset based on the old offset and the data set of statistical population under a constraint condition such that the new offset is obtained as a sum of the old offset and a correction vector,

wherein the correction vector is a linear combination of a set of second fundamental vectors, which are defined in principal axis directions of distribution of the data set of statistical population, and wherein respective coefficients of the linear combination of the second fundamental vectors are obtained by weighting respective coefficients of a temporary position vector of a temporary offset relative to the old offset according to a ratio of principal values of the distribution of the data set of statistical population, said temporary offset being derived from the data set of statistical population without using the old offset and said temporary position vector being a linear combination of the second fundamental vectors.