A wafer processing method for forming a via hole in a wafer. The wafer processing method includes a filament forming step of applying a pulsed laser beam to the wafer, the pulsed laser beam having a transmission wavelength to the wafer, in the condition where the focal point of the pulsed laser beam is set inside the wafer in a subject area where the via hole is to be formed, thereby forming an amorphous filament inside the wafer in the subject area, and an etching step of etching the amorphous filament formed inside the wafer by using an etching agent to thereby form the via hole inside the wafer.