Ignition device for exothermic welding comprising a metal container at least partially housable in a weld mold, the metal container comprising a top base closed by a cap, a bottom base and an inner chamber for housing a first welding material having an ignition temperature, and ignition means for triggering a first exothermic reaction in the first welding material intended for triggering a second exothermic reaction in a second welding material housed in the weld mold, wherein the metal container is an electrically conductive metal bushing housable in an electrically conductive top cap of the weld mold, which is designed for surrounding and contacting the metal bushing of the ignition device and which is connectable to a first pole of a power output of a voltage generator; the cap of the metal bushing is made of an electrically insulating material: characterised in that the bottom base of the metal bushing has an opening through which the first welding material falls in an incandescent state towards the second welding material housed in the weld mold when the first exothermic reaction has been triggered; the inner chamber comprises an inner wall sized for housing the first welding material in the form of a solid pellet and suitable for placing the pellet of the first welding material in electrical contact with the inner wall of the inner chamber; the ignition means comprise an electrode that goes through the cap of the metal bushing and comprises a top contact connectable to a second pole of the power output of the voltage generator, and a bottom contact in the form of a filament that can be in electrical contact with the pellet of the first welding material; the filament is made of a material having a melting temperature greater than the ignition temperature of the first welding material; a contact-assuring element assuring electrical contact of the pellet of the first welding material with the filament is supported on the bottom base of the metal bushing, wherein the electrical contact-assuring element comprises a coil spring which is guided into the inner perimeter of the inner chamber and compressed by the pellet of the welding material when said pellet is housed in the inner chamber (1 c) of the metal bushing before the exothermic reaction and released when the welding material gradually falls in an incandescent state towards the weld mold through the opening of the bottom base of the metal bushing. characterised in that the bottom base of the metal bushing has an opening through which the first welding material falls in an incandescent state towards the second welding material housed in the weld mold when the first exothermic reaction has been triggered; the inner chamber comprises an inner wall sized for housing the first welding material in the form of a solid pellet and suitable for placing the pellet of the first welding material in electrical contact with the inner wall of the inner chamber; the ignition means comprise an electrode that goes through the cap of the metal bushing and comprises a top contact connectable to a second pole of the power output of the voltage generator, and a bottom contact in the form of a filament that can be in electrical contact with the pellet of the first welding material; the filament is made of a material having a melting temperature greater than the ignition temperature of the first welding material; a contact-assuring element assuring electrical contact of the pellet of the first welding material with the filament is supported on the bottom base of the metal bushing, wherein the electrical contact-assuring element comprises a coil spring which is guided into the inner perimeter of the inner chamber and compressed by the pellet of the welding material when said pellet is housed in the inner chamber (1 c) of the metal bushing before the exothermic reaction and released when the welding material gradually falls in an incandescent state towards the weld mold through the opening of the bottom base of the metal bushing.