A polishing apparatus has a turntable and a top ring for gripping a semiconductor wafer to be polished by an abrasive cloth on the turntable. The polishing apparatus incorporates a loading and unloading unit having a supply holder for holding and supplying a semiconductor wafer to be polished to the top ring at a transfer position, and a reception holder for receiving a polished semiconductor wafer from the top ring at the transfer position. The reception holder and the supply holder are mounted on respective opposite ends of a support block which is angularly movable in a vertical plane by a turning mechanism for moving the supply holder and the reception holder alternatively to the transfer position.