An encoder unit comprising an object to be detected having a track having a first region with a magnetization pattern at a predetermined pitch and a second region having no periodic magnetization pattern, and a detector having a magnetoresistance effect element arranged in the direction which intersects the direction of the magnetic flux of the magnetization pattern and in opposed relationship with the object to be detected. The encoder unit is simple in construction yet capable of detecting the position of the object to be detected with a higher degree of accuracy than conventional encoders.