A silicon dioxide film removing method is capable of removing a silicon dioxide film, such as a natural oxide film or a chemical oxide film, at a temperature considerably higher than a room temperature. The silicon dioxide film removing method of removing a silicon dioxide film formed on a workpiece in a processing vessel 18 that can be evacuated uses a mixed gas containing HF gas and NH3 gas for removing the silicon dioxide film. The silicon dioxide film can be efficiently removed from the surface of the workpiece by using the mixed gas containing HF gas and NH3 gas.