Disclosed is a piezoelectric speaker including: a piezoelectric layer that converts electrical signals into oscillation and outputs sound; an electrode that is formed on a top or a bottom of the piezoelectric layer to apply the electrical signals to the piezoelectric layer; an acoustic diaphragm that is made of a hetero material including a first acoustic diaphragm and a second acoustic diaphragm and is attached to the bottom of the piezoelectric layer on which the electrode is formed; and a frame attached in a form enclosing a side of the acoustic diaphragm.