PURPOSE: To perform the advance and retreat control of a travelling robot inside a pipe together with the travelling control, by linking 1st and 2nd cam parts corresponding to the two operational positions of a direction changeover valve to the operation part of the direction changeover valve having in the peripheral direction alternately.

CONSTITUTION: A piston rod 61 of an operation cylinder 6 is projected and retracted according to the feeding and feeding stoppage operations of a pressure fluid to fluid pressure motors m1, m2. When the piston rod is projected, then, a rotating member 7 is subjected to rotation operation. This rotation operation is transmitted to a cam member linked to the rotating member with its interlocking, the cam member is rotated and also the part linked to the operation part V1a of a direction changeover valve V1 is changed to a 2nd cam part 8a from a 1st cam part 81. A once directional changeover is thus caused with once feeding operation. Then, the direction changeover valve keeps the original position at this time without the rotating member being turned for the retreat motion of the piston rod. Namely the direction changeover valve is switched once when the feeding and feeding stoppage of the pressure fluid being performed.