The present invention pertains to: a method for arc spot welding a steel plate having a carbon equivalent CeqBM of 0.35 or more (the carbon equivalent CeqBM is defined in the specification) and containing 0.35 mass % or more of C, the method being characterized by forming a weld metal having a structure in which the proportion of an austenitic structure exceeds 80%; and a welding wire suitable for being used therefor. According to the arc spot welding method, brittle fracture can be prevented and high joint strength can be obtained even when the C content in the steel plate is high.