The dynamics of a segregation pattern for a granular mixture in a highly filled rotating drum were studied. A spontaneously segregated band pattern traveled laterally and was accompanied by the repeated creation of new bands near the center of the drum and annihilation at both of its ends. The presence of nearly stationary convection plays an essential role in causing this traveling wave. Based on direct observations of both the interior and the exterior of the segregation pattern, this spatiotemporal pattern is interpreted in terms of a one-dimensional Cahn-Hilliard equation by including the effect of stationary convection.