Abstract: A moving position detector suitable for use as a lightweight, thin mouse. Rotations generated by virtue of frictional forces generated between a bottom of a rotating body and a floor surface are detected by a rotation detecting means as the number of rotations of a rotary encoder portion and converted into an output signal corresponding to the signal from the encoder portion for output to an output means for input into a computer. The rotating body has a pressurizing point for applying loads by gravity or a mechanical element to positions other than a center on the bottom in a direction normal to a moving direction of a mouse relative to the shaft.