A piezoelectric actuator comprising an elastic plate 2 with a projection 3 provided on one of both surfaces of the plate. A first pair of strip-like piezoelectric elements 120a, 120b are fixed to the other of both the surfaces of the plate such that each of the first pair of piezoelectric elements is disposed along a first straight line passing through the position of the projection on a respective one of its opposite sides. A second pair of strip-like piezoelectric elements 122a, 122b are fixed to the same surface of the plate as the first pair of piezoelectric elements 120a, 120b such that each of the second pair of piezoelectric elements is disposed along a second straight line passing through the position of the projection perpendicular to the first straight line on a respective one of opposite sides of the position of the projection. Voltages are arranged to be applied to the respective piezoelectric elements of the first and second pairs as required so as to deform the plate, thereby causing the projection to deviate.