A piezoactuator for injecting fuel with a predetermined fuel pressure has an at least laterally narrowing casing around the internal space of the actuator which has a first temperature- and/or pressure-dependent volume change, a piezo stack located in the internal space which has a second temperature- and/or pressure-dependent volume change, a transmission element which is located between the piezo stack and the casing for transmitting the fuel pressure on the outside of the casing onto the piezo stack, wherein the transmission element has a passivating liquid which has a third temperature- and/or pressure-dependent volume change as well as several preformed bodies which have a fourth temperature- and/or pressure-dependent volume change; wherein the relation between the passivating liquid and the preformed bodies is set that the first volume change of the casing basically corresponds to an overall internal space volume change which has at least the second, third, and fourth volume change.