Multi-axis industrial robot, comprising: - a base structure, - an articulated robot wrist, and - a chain of mutually articulated robot elements (13, 14, 16, 18) connecting said base structure to said robot wrist, - wherein said robot wrist ends with a flange to which is rigidly connected an electric spot welding head that requires a power supply and/or a fluid supply, - wherein the welding head comprises a supporting structure rigidly connected to the robot wrist, and a pair of welding electrodes (101, 102) carried by respective electrode-holding arms (103, 104), wherein at least one of said electrode-holding arms is movably mounted on the support structure of the head between an open position and a closed position, said head further comprising an actuator for driving said movable arm and an electrical transformer for the application of a welding electrical voltage to the electrodes (101, 102), - wherein, through said chain of mutually articulated robot elements (12, 13, 14, 16, 18) and through said robot wrist a continuous internal passage is defined in which one or more cables and/or pipes for said power supply and/or said fluid supply to the tool are received, - wherein the structure of the welding head is completely covered by a casing consisting of two half-shell sides (105a, 105b) coupled to each other and having main walls parallel to the general plane of the two electrode-holding arms, said casing having a rear opening for the connection of the supporting structure of the welding head to the flange of the robot and a front opening from which the two electrode-holding arms (103, 104) of the welding head protrude, - and wherein said supply cables and preferably also said pipes, which are received through the continuous internal passage of the robot, continue further without interruption through a passage formed in said flange and then inside said structure of the welding head up to a connector input provided on said transformer, whereby the said cables and pipes are arranged completely inside the robot and inside the welding head, without the need to provide separate cables or pipes for the welding head connected to the cables and the pipes of the robot in correspondence to said flange. - a base structure, - an articulated robot wrist, and - a chain of mutually articulated robot elements (13, 14, 16, 18) connecting said base structure to said robot wrist, - wherein said robot wrist ends with a flange to which is rigidly connected an electric spot welding head that requires a power supply and/or a fluid supply, - wherein the welding head comprises a supporting structure rigidly connected to the robot wrist, and a pair of welding electrodes (101, 102) carried by respective electrode-holding arms (103, 104), wherein at least one of said electrode-holding arms is movably mounted on the support structure of the head between an open position and a closed position, said head further comprising an actuator for driving said movable arm and an electrical transformer for the application of a welding electrical voltage to the electrodes (101, 102), - wherein, through said chain of mutually articulated robot elements (12, 13, 14, 16, 18) and through said robot wrist a continuous internal passage is defined in which one or more cables and/or pipes for said power supply and/or said fluid supply to the tool are received, - wherein the structure of the welding head is completely covered by a casing consisting of two half-shell sides (105a, 105b) coupled to each other and having main walls parallel to the general plane of the two electrode-holding arms, said casing having a rear opening for the connection of the supporting structure of the welding head to the flange of the robot and a front opening from which the two electrode-holding arms (103, 104) of the welding head protrude, - and wherein said supply cables and preferably also said pipes, which are received through the continuous internal passage of the robot, continue further without interruption through a passage formed in said flange and then inside said structure of the welding head up to a connector input provided on said transformer, whereby the said cables and pipes are arranged completely inside the robot and inside the welding head, without the need to provide separate cables or pipes for the welding head connected to the cables and the pipes of the robot in correspondence to said flange.