A fuselage spar for aircraft is vertically mounted between an upper surface panel and a lower surface panel of the fuselage at the junction between a first wing structure spar and a second wing structure spar symmetrical with the first wing structure spar relative to the fuselage, and comprises peripheral zones and a central zone. This fuselage spar comprises a hollowed-out portion in the central zone, the peripheral zones of the spar providing for a draining of the normal loads conveyed by the wing structure spars. Also disclosed is a central spar box comprising such a spar.