While various types of locomotion mechanisms are available for robots, this research focuses on developing a biped walking robot. The robot uses a soft, balloon-like structure for its body and incorporates buoyancy. We achieved the walking movement by a manual ON-OFF control of actuators, however, the relationship between the control signals and a gait has not been clarified yet. In this paper, we performed experiments by an automated ON-OFF control to analyze the leg joint angles and a position in the center of gravity(COG) using a motion analysis software. We also estimate a role of posture control in the gait control.