A fuel injector comprising: an injection valve provided with a mobile needle to regulate the fuel flow; an actuator adapted to shift the needle; an injection nozzle; a supporting body having a tubular shape and displaying a feeding channel; a sealing body provided with a valve seat of injection valve and comprising a disc-shaped capping element, which lowerly and fluid-tightly closes the feeding channel and is crossed by the injection nozzle, and a guiding element, which rises from the capping element, has a tubular shape, and accommodates the needle therein; an external fuel guiding channel defined between the feeding channel and the guiding element; a number of through feeding holes obtained in the lower part of the guiding element and leading towards valve seat; and a shutter head having an essentially spherical adjustment zone, which is integral with the needle, externally engages the guiding element.