Abstract: A humidifying device includes a casing that defines a first air passage that guides air to an adsorbent module accommodation portion accommodating an adsorbent module including an adsorbent, and a second air passage through which the air flowing out of the adsorbent module accommodation portion flows. The humidifying device includes a peltier device that has a heat absorbing side and a heat generating side generating heat due to heat transfer from the heat absorbing side. The peltier device is housed in the casing such that the heat generating side is located in the first air passage and the heat absorbing side is located in the second air passage.