This paper proposes a trajectory generation method for mobile robot by extending the trajectory segment iteratively. Considering the practical uses of the mobile robot like service purpose in the real world, it requires that the trajectory planning is done adaptively by depending on the situation changes. For that, designated waypoints for future motion are given sequentially from the environment recognition process and thus trajectory generation should be processed in dynamical situation. In this paper, we described an iterative extension of the polynomial-based trajectory by considering the designated waypoint, the continuity with the existing trajectory segment and the stoppage constraint at the end of each trajectory segment. Proposed method provides the next trajectory segment for a certain period by referring to these conditions. Resultantly, iteratively generated trajectory segments connect each other smoothly and organize a single continuous trajectory. Computer simulations with proposed method were conducted and the results were shown. They showed proposed method realizes trajectory generation based on sequential extension of the trajectory segment.