To disclose a magnetic encoder being subjected to only small gap variation between a magnetic sensor element and a magnetic medium and readily assembled, and having a smaller number of components, high sliding resistance, and high stability against outside force, such as shock or the like. The magnetic sensor holding mechanism has a swirling spring plate structure having elasticity with respect to rotation around a rotation axis in a reciprocative slide relative movement direction, elasticity with respect to rotation around a rotation axis in a direction perpendicular to the reciprocative relative movement direction and in parallel to the magnetic medium, and elasticity in the direction perpendicular to the sensor element. A load between 50 mN and 80 mN is applied to press onto the magnetic medium.