By resistor attached by a piezoelectric element, measurement with high accuracy is possible by strain of the piezoelectric element. A piezoelectric actuator includes the piezoelectric element which is formed into an arbitrary shape, polarized in an arbitrary direction, and includes electrodes provided on at least two surfaces opposed in a thickness direction thereof. The piezoelectric actuator also includes a driver power supply for applying a voltage between the electrodes to generate strain in the piezoelectric element, a driver power supply for applying a voltage to generate strain in the piezoelectric element, resistors provided on the electrodes through intermediation of insulators, and a displacement detection device connected with the resistors. The electrodes of the piezoelectric element on which the resistors are provided are set at a ground potential.