Disclosed are a cathepsin E gene and a non-human mammalian animal with the cathepsin E-associated gene altered. The cathepsin E-associated gene and the DNA fragment thereof have each a base sequence or a partial amino acid sequence as identified by SEQ ID #1. The cathepsin E-associated gene-altered non-human mammalian animal according to the present invention, such as a cathepsin E-associated gene-altered mouse or the like, has the functions of the cathepsin E-associated gene by performing homologous recombination with a targeting vector having two homologous recombination regions, the first homologous recombination region being composed of a DNA fragment of approximately 1.2 kbp present on the 5'-upstream side of exon 1 and the second homologous recombination region being composed of a DNA fragment of approximately 7.0 kbp present on the 3'-downstream side of exon 4. The cathepsin E-associated gene-altered non-human mammalian animals according to the present invention can be used effectively for clarification of allergic diseases such as atopic dermatitis and so on as well as their disease conditions, and they are expected to be utilized as an experimental animal model for use with experiments on learning disabilities or memory impairments or acceleration of fighting episodes. Moreover, the cathepsin E-associated gene-altered non-human mammalian animal of the present invention is expected to be useful for the elucidation of the physiological functions about stress because it has a very high sensitiveness against stress.