A wave generator for a strain wave gearing (30, 30A), in which the wave generator is configured to cause an external gear of the strain wave gearing (30, 30A) that is capable of flexing in a radial direction to flex in a non-circular shape, to cause the external gear to partially mesh with a rigid internal gear (32, 33) of the strain wave gearing (30, 30A), and to cause a position where the external gear meshes with the internal gear (32, 33) to move in a circumferential direction in conjunction with rotation, the wave generator for the strain wave gearing (30, 30A) comprising: a rigid plug provided with a plug-outer-circumferential surface having a non-circular shape, and an annular displacement body provided with a plurality of radially arranged displacing sections, wherein each of the displacing sections is a rigid body in a radial direction of the annular displacement body and is connected so as to be able to elastically displace in the radial direction relative to the displacing sections adjacent thereto, wherein each of the displacing sections is provided with a plug-contacting section in a state of sliding contact with the plug-outer-circumferential surface of the plug, and an external-gear-contacting section for flexing the external gear in the non-circular shape, wherein the plug-contacting sections are positioned on an inside in the radial direction with respect to the external-gear-contacting sections; wherein the displacing sections are linearly extending fins which are arranged at equiangular intervals and have the same cross section and the same length; wherein inner end sections in a radial direction of the fins are the plug-contacting sections; wherein outer end sections in the radial direction of the fins are the external-gear-contacting sections; and wherein the outer end sections of the fins arranged adjacent to each other are connected to each other by an arcuate plate capable of flexing in the radial direction characterized in that the annular displacement body is fabricated from a single tape-shaped plate material having a specified width and a specified thickness, which has been folded in a direction perpendicular to a plate surface thereof at a specified interval; and in that the annular displacement body is provided with a plurality of layered fins, wherein each fin has a structure in which two sheet materials are layered, and external-gear-contacting sections as top end sections of adjacent layered fins are connected to each other by flat plate portions. a rigid plug provided with a plug-outer-circumferential surface having a non-circular shape, and an annular displacement body provided with a plurality of radially arranged displacing sections, wherein each of the displacing sections is a rigid body in a radial direction of the annular displacement body and is connected so as to be able to elastically displace in the radial direction relative to the displacing sections adjacent thereto, wherein each of the displacing sections is provided with a plug-contacting section in a state of sliding contact with the plug-outer-circumferential surface of the plug, and an external-gear-contacting section for flexing the external gear in the non-circular shape, wherein the plug-contacting sections are positioned on an inside in the radial direction with respect to the external-gear-contacting sections; wherein the displacing sections are linearly extending fins which are arranged at equiangular intervals and have the same cross section and the same length; wherein inner end sections in a radial direction of the fins are the plug-contacting sections; wherein outer end sections in the radial direction of the fins are the external-gear-contacting sections; and wherein the outer end sections of the fins arranged adjacent to each other are connected to each other by an arcuate plate capable of flexing in the radial direction characterized in that the annular displacement body is fabricated from a single tape-shaped plate material having a specified width and a specified thickness, which has been folded in a direction perpendicular to a plate surface thereof at a specified interval; and in that the annular displacement body is provided with a plurality of layered fins, wherein each fin has a structure in which two sheet materials are layered, and external-gear-contacting sections as top end sections of adjacent layered fins are connected to each other by flat plate portions.