A host device exchanging information with a memory card, the host device including: a charge management module configured to receive payment of a charge corresponding to an increased amount of a usable area if a capacity of the usable area of the memory card for saving user data is increased, and pay out a charge corresponding to the reduced amount of the usable area if the capacity of the usable area is reduced; and a transmission module configured to transmit an area changing command to instruct an increase or a reduction of the usable area in accordance with the charge to the memory card.