The present invention provides: a solid-phase spot-welding method with which the welding temperature can be controlled accurately and with which a reduction in the welding temperature can be achieved, regardless of the type of metal material being welded; and a solid-phase spot-welding device that can be used suitably in this solid-phase spot-welding method. This solid-phase welding method involves overlapping metal plate materials and carrying out spot-welding, and is characterized by having a welding preparation step in which two or more metal plate materials are held in a state in which same overlap one another, thereby forming an interface to be welded, a temperature-raising step in which a pair of electrodes are used and the interface to be welded is heated by supplying a current by a direct method, an indirect method, or a series method, thereby forming a softened region in the vicinity of the interface to be welded, and a stress application step in which an external stress greater than or equal to the yield strength of the metal plate materials at a desired welding temperature is applied to the softened region, wherein the metal plate materials are welded to each other by subjecting the softened region to local deformation.