A piezoelectric actuator comprising an optimum layer structure when (100) orientation strontium ruthenate is used as a bottom electrode is provided. This piezoelectric actuator comprises a diaphragm 30 that is constituted by (100) orientation yttria-stabilized zirconia, CeO.sub.2, or ZrO.sub.2, that is grown epitaxially on a (100) orientation Si substrate 20, a buffer layer 41 formed on the diaphragm and constituted by (001) orientation REBa.sub.2Cu.sub.3O.sub.x, a bottom electrode 42 formed on the buffer layer and constituted by (100) orientation strontium ruthenate, a piezoelectric layer 43 formed on the bottom electrode and constituted by (100) orientation PZT, and a top electrode 44 formed on the piezoelectric layer.