Dissimilar-metal joining tool

A dissimilar-metal joining tool that places a ring-shaped joining auxiliary member made of iron, on a surface of a workpiece in which a second metal plate made of non-ferrous metal is disposed on a first metal plate made of iron in a laminated state, coaxially with a through-hole provided so as to penetrate through the second metal plate in a plate thickness direction, and that performs arc welding toward an inner hole of the joining auxiliary member, the dissimilar-metal joining tool comprising:

• a base that is attached to a distal end of a robot;
• an arc welding torch that is attached to the base;
• a positioning mechanism that is provided in the base, and that places the inner hole at a joining position in front of the arc welding torch and holds the joining auxiliary member in a positioned state in radially direction of the joining auxiliary member;
• and
• a pressing mechanism that presses the joining auxiliary member, which is held by the positioning mechanism, in the vicinity of an outer peripheral edge of the joining auxiliary member and in a thickness direction.