In a legged mobile robot, an elastic member is installed at a position between a second joint connecting a distal end of a leg and a foot and a floor contact end of the foot, and a displacement sensor is installed in a space defined by a top-to-bottom height of the elastic member. Channel signals having the same characteristics are generated by the switching operation of a second switch from a received channel signal received by an antenna selected by a first switch, and the thus generated signals are input to the respective receiver circuit systems. The control unit controls the rotational speed of the rotating polygonal mirror by accelerating or decelerating the drive unit at a predetermined time during one rotation of the rotating polygonal mirror.