The author studied the change in relative humidity within a showcase from the static and dynamic points of view. The moisture absorption and desorption capacity on which the static humidity characteristic of the system depends was estimated by moisture gain and loss at absorbing and desorbing stages respectively. Three humidity controlling agents -- A type (RD) silica gel, Nikka pellet, and Artsorb -- were compared and Art-sorb proved to have the greatest capacity. Placing the controlling agent in a limited part of the case delays the overall humidity control throughout the case due to slow diffusion of the moisture. In order to improve the disadvantage, the author used a fan to circulate the air inside the case, and in a second experiment put a sheet with silica gel incorporated between the fibers on the rear internal wall of the case, and obtained fairly successful results in both cases. See 15-1074 and 18-914. -- AATA