PURPOSE: To enable normal control regardless of aged elongation of a position detecting line element by providing a control means for correcting a detected value of a position detector according to the output of a detector depending on the displacement of a mover caused by elongation of the line element.

CONSTITUTION: A position detector 6 which is operated by a line element 9 extended along the moving path of an industrial robot 3 on a travel base 1 to detect the industrial robot 3 is provided. Further, an elongation detector 13 is formed by a mover to which the end part of the line element 9 is connected, which is movably engaged with the base and a detector for generating an output depending on the travel distance of the mover. A detected value of the position detector 6 is corrected according to the output of the detector by means of a control device 21.