Abstract: A wave gear drive having a wave generator whose exterior configuration is formed using a shape defined by a tangential polar coordinate equation having at least four Fourier expansion terms, whereby the amount of flexing of the flexible external gear can be maintained at a prescribed magnitude while simultaneously reducing the magnitude of the tooth rim bending stress of the external gear, and the meshing entry gap of the teeth can be enlarged, thus eliminating the danger of tooth interference. The wave gear drive exhibits high load capacity and excellent gear meshing performance.