In this study, we report about mechanisms of a biped walking robot ISR-1 (Inner Skeleton type Robot 1) . We have developed a light weight robot applied the inner skeleton frames and cooperative motion of two or three actuators for one degree of freedom. Total degrees of freedom are 18 degrees. Each joint of the robot is driven by 16 actuators. Main actuator is screw cylinder type actuator that gives liner motion. This robot equips with two gyros on head and six force sensors at feet for balance control. We have confirmed walking possibility of the robot.