To provide a motor of which high performance can be achieved while a high strength being achieved.SOLUTION: A lifter motor comprises a motor body which rotationally drives a rotary shaft, and a deceleration part which decelerates and outputs rotation of the rotary shaft. The deceleration part has an external gear 13 which has an external tooth 13b extending radially outward and which performs circular motion without performance of autorotation, and an output member 15 including an internal gear 15c which has an internal tooth 15d projecting radially inward and which is rotated in such a manner that the external tooth 13b is engaged with the internal tooth 15b by circular motion of the external gear 13. The external tooth 13b and the internal tooth 15d are formed into a shape having a curve of a cycloid viewed from an axial direction, and are so set as not to respectively contact a base end part on an engagement side in such a manner that tips 13c, 15c of both teeth are so made as to have a projection amount smaller than the curve of the cycloid.SELECTED DRAWING: Figure 4
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