A heat exchanger element includes partition members that include first gas passages that are passages for first gas and second gas passages that are passages for second gas and that are provided above the first gas passages, the partition members operative to partition the first gas passages and the second gas passages; spacing members that form the first gas passages and the second gas passages and that maintain a gap between the partition members; and an adhesive that adheres the partition member and the spacing member with each other. At least one of the partition member and the spacing member is made of a liquid absorbing material, and the adhesive is a water solvent adhesive in which water-soluble flame retardant is impregnated.