A gripping device constituting a welding device has a first contactor and a second contactor, which face each other and come in contact with a material to be welded. The first contactor vibrates at a predetermined vibration frequency under the effect of a first vibrator. The second contactor may be configured so as to be vibrated by a second vibrator. In this case, it is preferable that the first contactor and the second contactor are vibrated at different vibrational frequencies. In the abovementioned configuration, the first contactor and the second contactor periodically repeat contact with and separation from the material to be welded. In this state, the gripping device moves in the welding direction and welding is carried out on the material to be welded.