An apparatus for treating a surface of a wafer includes a wafer-holding device for holding the wafer horizontally at the center of the lower surface of the wafer to rotate the wafer around a predetermined rotation axis and a nozzle for supplying a flow of treatment liquid to the upper surface of the wafer held by the wafer holding device. The nozzle includes a supply member for supplying the treatment liquid at a predetermined flow speed at a predetermined position located higher than the upper surface of the wafer, and a member for changing the flow speed of the treatment liquid to a smaller speed at the predetermined position and providing a flow speed component in a direction parallel to the upper surface of the wafer. The flow speed of the treatment liqid at the predetermined position is thus controlled and the treatment liquid flow reaches the wafer upper surface with a speed component parallel to the upper surface of the wafer. The speed of the treatment liquid flow is kept sufficiently small so that the treatment liquid reaching the wafer does not cause unevenness on the wafer. Since the treatment liquid flow has a speed component parallel to the upper surface of the wafer it spreads over the wafer smoothly. In another aspect of the invention, the rotation axis is spaced from an axis of the supply member.