The present disclosure provides a roller assembly including: a support base provided with a shaft hole; and at least two circular arc segments that are detachably mounted on the support base, wherein the at least two circular arc segments constitute a roller and a vertical distance from any point on periphery of the roller to an axis of the shaft hole is larger than a vertical distance from any point on periphery of the support base to the axis of the shaft hole. The present disclosure also provides a transmission device including a roller assembly described above.