To realize smooth bipedality similar to a walking mode of a human by a simple and inexpensive constitution.

Each of foot parts 40 and 50 draws an elliptical trail and performs a rotary motion so that left and right sides may be put into opposite phases by a substantially parallelogram crank mechanism of both of leg parts 20 and 30 of a robot main body 1. Both of the foot parts 40 and 50 are provided with forks 44 and 54 which are rotatable within a substantially horizontal surface with a vertical shaft as a center and are energized so as to be extended inward and substantially straight. When the foot part 50 is lifted and fed forward by driving the leg parts 20 and 30, the fork 54 is rotated to a rear side and saved by being pushed by a case 42 of the other foot part 40 when the fork 54 is brought into contact with the case 42. When the foot part 50 is moved forward and the fork 54 is not brought into contact with the case 42, the fork 54 is returned to a position extended inward again by energizing force. Since support by one-leg of a body part 10 is attained by the fork 44 in the foot part 40, forward propelling force is obtained by rotary motions of the leg parts 20 and 30.