An electrostatic actuator is provided which can increase the amount of displacement of a diaphragm, thereby improving the ejection pressure when employed as a drive mechanism in a droplet ejection head. The electrostatic actuator comprises: a first substrate having a diaphragm functioning as a first electrode; and a second substrate coupled to the first substrate and having a second electrode opposite the first electrode, wherein: the diaphragm is displaced with an electrostatic force generated by applying a voltage between the electrodes; and an insulation film is provided on a coupling surface of the first substrate which couples with the second substrate, and an area of the insulation film corresponding to the diaphragm has a reduced thickness region.