Magnetic members are arranged along a straight line and can be placed face-to-face with spin-valve magnetoresistive elements. The magnetic pole faces of the magnetic members which can be face-to-face with the spin-valve magnetoresistive elements have different magnetic polarities from the magnetic pole faces of neighboring magnetic members. The magnetic members are arranged at a uniform pitch. Each magnetic member is spaced from neighboring magnetic members. X/P is from 40% to 60%, where X is length of each magnetic member along an arrangement direction of the magnetic members, and P is pitch of the magnetic members along the arrangement direction.