Electrically-induced bending of Selemion IPMC is caused by the charge induced into the IPMC. This induced charge quantity is susceptible to the absolute humidity of environment. There are two types of charges, the charge causing bending and the rest of charge that causes no bending. In the high humidity environments, where absolute humidity is above 10 gm^-3, the quantity of charge causing no bending accounts for the large part of whole charge induced into the Selemion IPMC, while quantity of such charge is negligibly small at the absolute humidity of less than 10 gm^-3. Estimating the quantity of those two types of charges individually, we successively analyzed the bending stability of Selemion IPMC at the absolute humidity above 10 gm^-3. Consequently, we deduced the following conclusions. 1) There exists a large time delay in the current in response to the voltage input, 2) Current is highly dumping, and 3) Bending behavior is marginally stable under the input of any frequency.