Humidifier

A humidifier that can maintain high sealing performance between a separator and a water exchange membrane without applying an excessive external force to the separator even in the event of temperature change is provided. Humidifying modules each include plate-shaped separators each including a dry gas-side water exchange portion formed on one side and a water-containing gas-side water exchange portion formed on the other side. The humidifying module is structured by stacking a plurality of the separators in a state in which a water exchange membrane is disposed between the dry gas-side water exchange portion and the water-containing gas-side water exchange portion facing each other. A loop-shaped partition member that forms a pressurization space between the adjacent humidifying modules is provided in a state in which the humidifying modules are stacked to guide a fluid into the pressurization space.