To provide an adsorption dehumidifier capable of supplying air of a low dew point even with low-temperature desorption air.

The adsorption dehumidifier is adapted to cool and dehumidify outside air and to allow it pass through an adsorption zone 2 of a dehumidifying rotor 1. The dehumidifying rotor 1 includes two desorption zones which are a first desorption zone 3 and a second desorption zone 4. Outside air is heated to pass through the first desorption zone 3 containing much moisture, for desorption, and dry air flowing out of the adsorption zone 2 is allowed to flow to the second desorption zone 4 in the subsequent stage containing little moisture, for desorption. A purpose of supplying air of the low dew point with low-temperature desorption air is thereby achieved with a minimum number of components to enhance an energy-saving effect.