Encoder

An encoder including a magnetic medium and a magnetic sensor that is opposed to the magnetic medium with intermediary of a gap and moves relative to the magnetic medium, wherein

• the magnetic medium is magnetized in direction of the relative movement at a pitch λm,
• the magnetic sensor includes a plurality of 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 the reference position, the magnetoresistive elements as harmonic reducing patterns are disposed at following positions, with P(n) defined as an n-th prime, wherein n is a natural number,
• a position offset by λm/(2·P(n)) from the reference position toward at least one side of the direction of the relative movement in plan view, wherein N≧n>1 and N is a natural number satisfying N>2, and
• a position further offset by λm/(2·P(L+1)) from a position offset by λm/(2·P(L)) from the reference position toward at least the one side of the direction of the relative movement in plan view, wherein P(L) is an L-th prime and L is a natural number satisfying 1<L<N, and
• x satisfying P(N+1)<x and x≠P(k), wherein k is a natural number satisfying 1<k, is set and the magnetoresistive elements as the harmonic reducing patterns are disposed at following positions,
• a position offset by λm/(2x) from the reference position toward at least the one side of the direction of the relative movement in plan view, and
• a position further offset by λm/(2x) from the position offset by λm/(2·P(L)), wherein 1<L<N, from the reference position toward at least the one side of the direction of the relative movement in plan view.