A piezoelectric device for an injector is built into an injector and generates driving force of the injector. A relation d(0.1Ec)/d(1.2Ec)≧0.50 is established between an apparent piezoelectric constant d(1.2Ec) calculated from static elongation when an electric field of 1.2Ec is applied to the piezoelectric device in the same direction as a polarizing direction while a preset load of 500 N is applied to the piezoelectric device, and an apparent piezoelectric constant d(0.1Ec) calculated from static elongation when an electric field of 0.1 Ec is applied to the piezoelectric device in the same direction as the polarizing direction. The piezoelectric device so fabricated has high durability and can be used for a long time.