The present invention is directed to a humidity controlling ventilator which takes in air through the use of an air blowing fan, and controls the humidity of the taken air via an adsorption heat exchanger prior to supplying it to the room. In the invention, the air blowing fan is controlled so as to make an air volume flow rate approach a predetermined target volume flow rate. To do this, the invention calculates the fan's air volume flow rate based on a specific volume of air downstream of the adsorption heat exchanger and an air mass flow rate of the fan. The calculated value is fed to an air blow controller that is configured to control the fan such that the calculated air volume flow rate approaches the predetermined target air volume flow rate.