To provide an insulating film forming method employing a liquid drop discharging system appropriate for manufacturing a surface acoustic wave element piece.

In an insulating film forming method employing a liquid drop discharging system for forming an insulating film covering a pattern electrode of a uniform film thickness formed on a piezoelectric substrate, liquid drops of insulating film forming materials whose discharge amounts are controlled are selectively applied to an insulating film forming portion of metal wiring formed on the piezoelectric substrate by the liquid drop discharging system and to the piezoelectric substrate, and the insulating film forming portion and a non-forming portion are formed on the metal wiring. The insulating film forming materials use inorganic materials.