Several types of traditional wooden strage cases for scrolls and manuscripts such as inro, daisashi, kabusebuta, kendon, -case, and ole wooden safe, a plastic case for films, a packing case for transportation, and a small display case were investigated to examine their performance to regulate fluctuations of the ambient relative humidity. An experiment indicated that hygrometric half- times of well-constructed traditional wooden cases made of paulownia are between 2 and 6 days. The other cases had almost the same values except the wooden safe. An equation which describe the RH change inside cases was derived using these values. According to this the change would be reduced to less than 10per thousand of the ambient daily RH change and to less than 20per thousand of the five days periodical change, but there would be no over a period of one year.