DETECTING DEVICE FOR POSITION OF TRAVEL DEVICE

PROBLEM TO BE SOLVED: To accurately obtain a drift quantity even when a gap value is changed. SOLUTION: A pair of gap detecting coils 5a, 5b arranged above and below are installed above a pair of drift detecting coils 3a, 3b arranged in parallel on the same plane, and AC currents are fed to the gap detecting coils 5a, 5b. A metal mark plate 2 is installed on a travel road surface 1. The drift quantity (positional drift in the y-direction) between a travel device and the mark plate 2 is obtained based on the induced voltage difference of the drift detecting coils 3a, 3b. A gap value is obtained based on the induced voltage difference of the gap detecting coils 5a, 5b. The obtained drift quantity is corrected with the gap value by a gap correcting circuit 14, the corrected drift signal Szh not affected by the change of the gap value is obtained, and steering control is applied based on the corrected drift signal Szh.