There is provided a wheel motor device including a variable-rotation output unit for outputting rotational power of a variable-rotation output body accommodated in a variable-rotation output body housing via a variable-rotation output shaft rotating about a reference axis line; and a reduction unit including a reduction gear mechanism for reducing rotation speed of the variable-rotation output shaft and a gear housing for accommodating the reduction gear mechanism. The reduction gear mechanism includes an input shaft relatively non-rotatable about the reference axis line with respect to the variable-rotation output shaft; an eccentric member having a rotating center eccentric from the reference axis line, the eccentric member being relatively non-rotatable with respect to the input shaft; an outer teeth member supported at the eccentric member in a relatively rotatable manner, the outer teeth member having outer teeth arranged on the outer peripheral surface; an inner teeth member having an inner diameter greater than an outer diameter of the outer teeth member and fixed in a non-rotatable manner, the inner teeth member having an inner teeth engaging with the outer teeth, the inner teeth having a teeth number different from that of the outer teeth; a rotation-component retrieving mechanism for retrieving rotation-component around the reference axis line from the outer teeth member; and a reduced-rotation output member rotatably driven about the reference axis line by the rotation-component retrieving mechanism.