PURPOSE: To accurately position a traveling unit by specifying a fixed position along a track by markings to cause change in dielectric constant, etc., and obtaining a change signal corresponding to a fixed position by two sensors of the traveling unit.

CONSTITUTION: A fixed position 34 is specified by markings 18 and 20 to bring about change in magnetic permeability and dielectric constant of induction type namely capacitive type sensors 14 and 16 in detection regions. The two sensors 14 and 16 attached to a traveling unit generate analog signals corresponding to the markings 14 and 16, respectively. One signal of the two signals is subtracted from the other to give a change signal corresponding to the fixed position 34 to be reached.