A dehumidifier by which the rate of heat recovery by the heat exchanger for recovering heat can be increased, the power consumption of the heater can be decreased, and by which the amount of dehumidification per a power consumption can be promoted, is disclosed. The dehumidifier 1 comprises a rotor case 31 harboring a dehumidification rotor 2 rotatably and drivably mounted therein, having an opening for dehumidification 38 through which air to be dehumidified passes, and having an opening for regeneration 39 through which air for regeneration passes; a heater 5 for heating the air for regeneration before passing through the opening for regeneration; a heat exchanger for recovering heat 7 which transfers heat of the air for regeneration passing through the second passage section to the air for regeneration passing through the first passage section; a dehumidification passage X harboring a dehumidification fan 3; and a regeneration passage Y harboring a regeneration fan 4. The direction of rotation of the dehumidification rotor 2 is set such that the air for regeneration which passed through posterior area C of the dehumidification rotor flows into downstream portion in the second passage section, and that the air for regeneration which passed through anterior area H of the dehumidification rotor flows into upstream portion in the second passage section.