An object of the present invention is to provide a humidifying apparatus capable of improving the humidification efficiency while lowering the pressure loss of gas even when a low-pressure gas is used, and is suitably
usable for
fuel cells. The present invention relates to a humidifying apparatus for
fuel cells, fabricated by loading a
hollow fiber membrane element into a container such that the space communicating with the hollow side of the hollow
fiber membranes is isolated from the space communicating with the outer side of the hollow
fiber membranes, wherein (a) the inner
diameter of the
hollow fiber membrane is larger than 400 μm, (b) the
water vapor permeation rate (P′H2O) of the hollow
fiber membranes is 0.5×10−3 cm3 (STP) / cm2·sec·cm Hg or more, (c) the ratio (P′H2O / P′O2) of the
water vapor permeation rate to the
oxygen gas
permeation rate of the hollow fiber membranes is 10 or more, and (d) the elongation at tensile break of the hollow fiber membranes after hot
water treatment in hot water at 100° C. for 50 hours is 80% or more of that before the hot
water treatment; particularly, the present invention relates to a humidifying apparatus for
fuel cells where, if the
effective length of the
hollow fiber membrane element is L and the inner
diameter of the container into which the hollow fiber membrane element is loaded is D, L / D is 1.8 or more.