Rotation detector and a torque sensor

While only One located on the same axis line comprises a first and a second rotating body which can rotate relative to the other. Located in one the same axis as the rotation body of these rotating body, by being connected through a slide guide means 34 in one rotational body, the relative rotation limit for one of the rotary body and the axis includes a slider 33 moving in the direction is allowed. It includes a movable magnet 32 ​​which is fixed on the same axis on the slider 33, and a fixed-side magnets 31 which move is restricted to the other fixed to the same axis of the rotating body and axially. A movable magnet 32 ​​and the fixed-side magnet 31, the change in size of the magnetic force acting on the magnets in the axial direction by the position in the rotational direction of one of the magnets is changed relative to the position in the rotational direction of the other magnet It is magnetized to. And a detecting means for detecting a positional deviation amount in the rotational direction of the first rotor and the second rotor on the basis of the axial position of the slider 33.