HUMIDIFIER

The invention relates to a humidifier (1) which comprises a housing (2) having a housing interior (6) and a membrane stack (7). The membrane stack (7) has six side surfaces (12a, 12b, 13a, 13b, 14a, 14b) and can be inserted into the housing interior (6) in the longitudinal direction (LR). Two of the opposing side surfaces (14a, 14b) are hermetically sealed; dry cathode supply air (K-ZL) can flow through two further of the opposing side surfaces (12a, 12b); and moist cathode exhaust air (K-AL) can flow through two further of the opposing side surfaces (13a, 13b). An air chamber (16a, 16b, 17a, 17b) is formed between each of the side surfaces (12a, 12b, 13a, 13b) through which air can flow and the housing (2). According to the invention: two of the side surfaces (12a, 12b) through which air can flow are aligned transversely to the longitudinal direction (LR) and air can flow therethrough in the longitudinal direction (LR); and two other of the side surfaces (13a, 13b) through which air can flow are aligned parallel to the longitudinal direction (LR) and air can flow therethrough transversely to the longitudinal direction (LR).