A starting device for welding comprises a starting seat which is fixedly mounted in a welding machine, and a starting head which matches the starting seat in use. A vertical surface sliding trough is arranged in the starting seat. A sliding block is mounted in the vertical surface sliding trough in a front-and-back slidable manner. The front end of each of a left sidewall and a right sidewall of the vertical surface sliding trough is provided with an oblique edge trough. The middle part of the back end wall of the vertical surface sliding trough is provided with a starting trough. The middle part of the back end wall of the sliding block is provided with a starting projection block. An insertion trough with a frontward inlet is arranged at a middle part between the left shaft and the right shaft in the sliding block. The left side and the right side of the insertion trough in the sliding block are respectively provided with a left transverse surface sliding trough and a right transverse surface sliding trough. A left sliding arm and a right sliding arm are slidably mounted in the left transverse surface sliding trough and the right transverse surface sliding trough. One end, which is far from the insertion trough, of each of the left sliding arm and the right sliding arm extends outwards and is provided with a pushing oblique surface.