A sheet separator. The sheet separator includes a main body, a frictional member, and an elastic member. The main body is rotatable with a slot being longitudinally parallel to the moving direction of the medium. The frictional member is disposed in the slot and contacts the medium. When feeding, the medium exerts a first force on the main body through the frictional member. Moreover, the elastic member connects to the main body and exerts a second force thereon. According to the first force and the second force, the angle between the main body and the medium is adjusted.