A humidity conditioning method includes: the humidity-absorbing step of bringing a hygroscopic liquid containing a hygroscopic material into contact with a first mass of air so that the hygroscopic liquid absorbs moisture in the first mass of air; and the regeneration step of separating moisture from the hygroscopic liquid having absorbed moisture, wherein the regeneration step retains the hygroscopic liquid having absorbed moisture, bombards at least some of the retained hygroscopic liquid with ultrasound to generate misty droplets from the hygroscopic liquid having absorbed moisture, and removes the misty droplets to separate moisture from the hygroscopic liquid.