A fitting structure includes: a power transmission member circumferentially provided with first and second spaced teeth and receiving power transmitted; and a fitting member surrounding the power transmission member and having a first recess and a second recess receiving the first tooth and the second tooth respectively, to fit to the power transmission member. There is a larger distance between an external surface of the first tooth and an internal surface of the first recess than that between an external surface of the second tooth and an internal surface of the second recess. An elastically deformable buffer member is provided between the external surface of the first tooth and the internal surface of the first recess.