Centipede-type multi-legged robots can traverse rough terrain and are expected for disaster rescue operations. However, too many actuators make robots large and heavy, and make their control systems complicated. To solve these problems, the authors have developed a centipede-type robot which is composed of many leg mechanism units with a planar 4-bar link mechanism connected with passive revolute joints and have proposed a new control scheme to steer the robot with only phase difference between units. However, quantitative experimental validation has not been carried out. Thus, in this paper, the turning motion of the robot is accurately measured with an angular velocity sensor and an optical motion capture system. The measured results reveal that the proposed control scheme is correct on the turning direction while the measured turning radius is larger than that calculated with the proposed control scheme. Resultantly, this error of turning radius is caused by the variation of leg contact position and static friction due to the rolling motion of units.