PURPOSE: To precisely and stably maintain the pollution concentration in a tunnel by calculating and estimating the dead time occurring based on the ventilation process in the tunnel and performing the ventilation control containing it.

CONSTITUTION: Dead time estimating means 6 and 8 are provided to calculate and estimate the dead time after the start of the ventilation control until its actual effect is measured occurring based on the ventilation process in a tunnel. Values of the pollution concentration in the tunnel measured by VI meters 4a and 4b and the air speed in the tunnel measured by an anemometer 5 are inputted to the dead time estimating means 6 and 8. The ventilation control is performed by a dust collector air volume control means 7 and a means 9 to control the number of jet fans so that the pollution concentration in the tunnel is maintained at the preset target value while the estimated dead time is taken into consideration.