A magnetic medium is magnetized in the relative movement direction at a predefined pitch km and a magnetic sensor includes plural magnetoresistive elements whose electrical resistance value changes depending on a magnetic field at a place where the magnetoresistive element is disposed. A position where the magnetoresistive element is disposed is defined as a reference position and, in addition to the magnetoresistive element of this reference position, the magnetoresistive elements as harmonic reducing patterns are disposed at the following positions, with P(n) defined as the n-th prime: a position offset by λm/(2·P(n)) from the reference position toward at least one side of the relative movement direction, wherein N≧n>1 and N is a natural number satisfying N>3, and a position further offset by λm/(2·P(L+1)) from a position offset by λm/(2·P(L)), wherein 1