A fuel injector, especially an injector valve for fuel injection equipment in internal combustion engines, includes a piezoelectric or magnetostrictive actuator and a valve closing body, operable by an actuator with the aid of a valve needle, which cooperates with a valve seat surface to form a sealing seat, and a valve housing. The actuator is prestressed by a compression spring and, together with this, is surrounded by an actuator housing which is supported by fluid at both its ends.