To provide a control device for jet fans starting the jet fans in the rotating direction so that the blasting direction coincides with the direction of the wind flowing in a road tunnel even when no anemoscope is installed.

A plurality of jet fans 22-28 are arranged in the road tunnel, the contamination of air is detected by a contamination detecting means 30, and not all jet fans 22-28 are driven. The rotating directions of rotors are judged by rotating direction judging means 50-56 based on the time differences between the inter-phase voltages V1, V2, V3 appearing by the rotation of the rotors of three-phase induction motors when impellers are rotated by the wind flowing in the road tunnel 10. The rotating direction coinciding with the direction of the wind is determined by a rotating direction determining means 58 based on these signals, the number of the jet fans to be started and the start in the determined rotating direction are instructed by a control means 32 according to the signals of the contamination detecting means 30 and the rotating direction determining means 58, and the jet fans 22-28 are driven by a drive control means 34 according to the signals.