Double support phase is important for biped robots to achieve stable walking. In this research, a simple trajectory planning method using Linear Pendulum Mode (LPM) is proposed for double support phase. A biped robot is modeled by a pendulum in LPM. The walking stability is assured when the supporting point of LPM is set in the specific area. The area is shown clearly with Zero Moment Point (ZMP) in this paper. LPM is able to be applied to various motions since LPM uses a simple pendulum model. In this paper, a stop motion is described, for example. A pendulum has the dynamism that the COG velocity in the horizontal direction becomes 0 at particular points. LPM realizes natural stop motions using the dynamism.