PURPOSE: To predict and control the ventilation of a road tunnel.

CONSTITUTION: CO detectors CO-1 and CO-2, and VI detectors VI-1 and VI-2 are respectively laid in the vicinity of both pit mouths 1 and 2 in a road tunnel 3. In addition, an anemometer W and jet fans JF-1 to JF-6 are provided in the tunnel 3. Also, values detected with the CO detectors CO-1 and CO-2, VI detectors VI-1 to VI-2 and the anemometer W are outputted to and processed with a measurement signal processing device 10. The processed signal is, then, logically calculated with a ventilation control device 11. According to the result of the logical calculation in the device 11, the number of the jet fans JF-1 to JF-6 for operation is determined, depending upon the extent of contamination in the tunnel 3, and a signal representing the number is sent to a power device 12. As a result, the power device 12 actuates the jet fans JF-1 to JF-6 by the number corresponding to the signal.