A contact tip reforming device that is configured to reform a contact tip for arc welding where a head end side inner peripheral surface of a guide hole that guides a welding wire is worn because of use, the device comprising: a first die to which the contact tip is fixable; a second die disposed so as to face a head end side of the contact tip fixed to the first die; and a pressing machine that is configured to cause the first and second dies (2; 3) to approach each other and to separate from each other, wherein the second die is provided with: a processing hole configured to plastically deform the head end side of the contact tip, said processing hole being formed in a position corresponding to the contact tip fixed, in use, to the first die and gradually decreases in diameter with increasing distance from the first die; the contact tip reforming device being characterised in that, a core metal is disposed on a hole center line of the processing hole, having a circular shape a cross section of which conforms to a cross section of the guide hole, said core metal being configured to be inserted, in use, into the guide hole of the contact tip fixed to the second die with the first and second dies (2; 3) approaching each other, and in that on an inner peripheral surface of the processing hole, the following are provided: at least three projecting portions projecting inward of the processing hole, extending along the hole center line and situated at regular intervals in a circumferential direction of the hole center line; and in that recessed surface portions that are as many as the projecting portions, are each formed on an inner peripheral surface between the adjoining two projecting portions of the processing hole and are situated at regular intervals in the circumferential direction of the hole center line, and in that the projecting portions are structured so as to plastically deform, in use, the head end side of the contact tip by, when the contact tip is inserted into the processing hole by the approach of the first and second dies to each other by the processing machine, pressing the head end side of the contact tip toward the hole center line until it is in contact with the core metal while being in sliding contact with a head end side outer peripheral surface of the contact tip under a condition where the contact tip is out of contact with the recessed surface portions. a first die to which the contact tip is fixable; a second die disposed so as to face a head end side of the contact tip fixed to the first die; and a pressing machine that is configured to cause the first and second dies (2; 3) to approach each other and to separate from each other, wherein the second die is provided with: a processing hole configured to plastically deform the head end side of the contact tip, said processing hole being formed in a position corresponding to the contact tip fixed, in use, to the first die and gradually decreases in diameter with increasing distance from the first die; the contact tip reforming device being characterised in that, a core metal is disposed on a hole center line of the processing hole, having a circular shape a cross section of which conforms to a cross section of the guide hole, said core metal being configured to be inserted, in use, into the guide hole of the contact tip fixed to the second die with the first and second dies (2; 3) approaching each other, and in that on an inner peripheral surface of the processing hole, the following are provided: at least three projecting portions projecting inward of the processing hole, extending along the hole center line and situated at regular intervals in a circumferential direction of the hole center line; and in that recessed surface portions that are as many as the projecting portions, are each formed on an inner peripheral surface between the adjoining two projecting portions of the processing hole and are situated at regular intervals in the circumferential direction of the hole center line, and in that the projecting portions are structured so as to plastically deform, in use, the head end side of the contact tip by, when the contact tip is inserted into the processing hole by the approach of the first and second dies to each other by the processing machine, pressing the head end side of the contact tip toward the hole center line until it is in contact with the core metal while being in sliding contact with a head end side outer peripheral surface of the contact tip under a condition where the contact tip is out of contact with the recessed surface portions.