PURPOSE: To improve the reliability of ventilation control by promoting the setting of car numbers on the basis of a command of the number of driving units by the measured value of concentration of contamination and ventilating load for the ventilation control in a road tunnel, and compensating the unit number command value of feedback control.

CONSTITUTION: Contamination concentration value is inputted from a ventilating means 20 and a contamination concentration measuring means 30 in a road tunnel 10 and on the basis of this value, control operation takes place. In addition, on the basis of ventilation load in the tunnel 10, the minimum value of the number of units is set at each constant time by a setting value setting means 70 for ventilating means operating unit numbers. Then, a command value of ventilating means operating unit numbers from a feedback control means 50 is compensated so as not to make the operating unit numbers smaller than the minimum value of the setting means for the operating unit number setting value of the ventilating means 20. On the other hand, there is provided a ventilation stabilizing means 60 being outputted to the ventilating means 20. With this constitution, the worsening of the concentration of contamination is kept back, thus stable ventilation control can be done in this way.