PURPOSE: To maintain straight running properties during running, in an absorption movement type robot constituted to run through relative movement between outer and inner frames and vary a running direction through relative revolution.

CONSTITUTION: An expandable drive leg having a sucking means is arranged at each of outer and inner frames intercoupled so that relative revolution and relative movement in one-way are practicable is provided. A revolving gear 19 is arranged on one side of the outer and inner frame. A drive gear 20 connected to a motor for revolution is arranged on the other side. An expansion contraction drive device 22 formed in such a manner that the tip of an actuating rod 25 is movable forward and backward to and from the tooth of a revolving gear is provided. A pressure contact body 26 to the revolving gear is mounted on the tip of the actuating rod and the pressure contact body is provided on the tip side with at least a soft resilient deforming part 29.