A TIG welding device comprising: a clamp electrode capable of holding first and second members of base materials (W1, W2) in close contact with each other at a welding-target portion; a clamp raising/lowering rod for holding the clamp electrode; a torch body for holding a torch electrode removably attached thereto; a linear drive member for holding the torch body and the clamp raising/lowering rod and for moving those members linearly in parallel with an axial direction of the torch electrode; a welding power supply for supplying a current flowing within a closed circuit including the torch electrode and the welding-target portion, and a control section configured to control actuation of the linear drive member and control electrical current supply; characterized in that the clamp raising/lowering rod is vertically movable integrally with and detachable from the linear drive member, and that the control section is configured to control actuation of the linear drive member and control electrical current supply such that while a pressurizing force is being applied to the welding-target portion by the clamp electrode and while a forward end of the torch electrode is kept in contact with the welding-target portion, a voltage is applied to between the torch electrode and the welding-target portion by the welding power supply to start current supply within the closed circuit, and then, while continuing the pressurization onto the welding-target portion and the current supply within the closed circuit, the forward end of the torch electrode is separated from the welding-target portion so as to generate an arc between the torch electrode and the welding-target portion, whereby the welding-target portion is welded by heat of the arc, wherein the control section is configured to control actuation of the linear drive member such that the linear drive member is linearly moved between a first position for positioning the clamp electrode and the torch electrode farther from the welding-target portion, a second position for positioning the clamp electrode at its working position, a third position for bringing the forward end of the torch electrode into contact with the welding-target portion, and a fourth position for separating the forward end of the torch electrode from the welding-target portion by a specified distance suitable for generation of the arc. a clamp electrode capable of holding first and second members of base materials (W1, W2) in close contact with each other at a welding-target portion; a clamp raising/lowering rod for holding the clamp electrode; a torch body for holding a torch electrode removably attached thereto; a linear drive member for holding the torch body and the clamp raising/lowering rod and for moving those members linearly in parallel with an axial direction of the torch electrode; a welding power supply for supplying a current flowing within a closed circuit including the torch electrode and the welding-target portion, and a control section configured to control actuation of the linear drive member and control electrical current supply; characterized in that the clamp raising/lowering rod is vertically movable integrally with and detachable from the linear drive member, and that the control section is configured to control actuation of the linear drive member and control electrical current supply such that while a pressurizing force is being applied to the welding-target portion by the clamp electrode and while a forward end of the torch electrode is kept in contact with the welding-target portion, a voltage is applied to between the torch electrode and the welding-target portion by the welding power supply to start current supply within the closed circuit, and then, while continuing the pressurization onto the welding-target portion and the current supply within the closed circuit, the forward end of the torch electrode is separated from the welding-target portion so as to generate an arc between the torch electrode and the welding-target portion, whereby the welding-target portion is welded by heat of the arc, wherein the control section is configured to control actuation of the linear drive member such that the linear drive member is linearly moved between a first position for positioning the clamp electrode and the torch electrode farther from the welding-target portion, a second position for positioning the clamp electrode at its working position, a third position for bringing the forward end of the torch electrode into contact with the welding-target portion, and a fourth position for separating the forward end of the torch electrode from the welding-target portion by a specified distance suitable for generation of the arc.