PURPOSE: To perform levitation control of a carrier stably by correcting the gap length, detected through a detector, to be equal to a predetermined value based on the detected gap length every time when the carrier is fixed periodically on a rail through a fixing device.

CONSTITUTION: When a carrier travels, while being levitated, on a rail 1 then stops at a predetermined position and fixed to the rail 1, correcting operation is carried out. Assuming that the output Gb from a gap length detector 4 is reduced to 1.5V (normal level is 2V), for example, due to variation of characteristic of the gap length detector despite of actual gap length of 2mm. Although G=1.5V at the instance when a relay contact RY1a closes, a subtracting/ integrating circuit continues integration until Gr-G=0 is satisfied and balanced state is achieved at a time point when Gc1.33V. Consequently, output from a multiplier MPY goes to 2V (G=2V) and a corrected true value is obtained from the gap length detector 4.