In temper rolling, a shape defect known as longitudinal buckling sometimes occurs, resulting in the formation of wrinkles like those on a washboard. The direction of the crest line of the longitudinal buckling is parallel to the rolling direction. In this study, the analysis of longitudinal buckling is performed using the elementary theory of buckling. First, we calculate the material-roll contact ratio by Hertz's formulae. Next, we calculate the stress distribution in the material at the roll gap using the punch pressure during indentation by Prandtl's formulae. Furthermore, we calculate the wavelength of the waves formed by longitudinal buckling using the elementary theory of buckling. We find that the wavelength calculated from the analysis is in good agreement with that obtained experimentally in the literature. We conclude that the method of analysis is valid, and that the cause of longitudinal buckling is the surface roughness of the roll.