A protective film forming method for forming a protective film of resin on the front side of a wafer, where the method includes a step of holding the wafer on a spinner table in the condition where the front side of said wafer is oriented upward; a step of forming a water layer of a thickness of between about 1 mm and about 3 mm to cover the front side of the wafer; a step of dropping a liquid resin onto the water layer at the center of the wafer; and a step of rotating the spinner table to rotate the wafer held on the spinner table, thereby scattering the water layer and radially spreading the liquid resin dropped on the water layer to form a first resin film covering the front side of the wafer by a centrifugal force produced during rotation of the wafer.