To provide an air current investigating device capable of investigating the state of an air current by a simple device to air-conditioning equipment installed in a general building.

The air current investigating device (10) includes a tracer supply device (20) including a tracer supply pipe (23) for supplying a tracer (21) and a tracer outlet (24) disposed at a tip of the tracer supply pipe for blowing off the tracer (21) at the inside of a duct (64), an image pick-up device (30) for continuously picking up images of the tracer (21) blown off into a room (61) from a blow-off port (65), and a searching device (40) for searching a blow-off range on the basis of image data picked up by the image pick-up device (30). The tracer outlet (24) is installed in a position far from the blow-off port (65) so that the tracer (21) from the tracer outlet (24) is sufficiently expanded in the duct (64).