A mobile terminal system is provided whereby, when a memory card or memory card with an IC function inserted in a mobile terminal apparatus is removed, a function of at least one of the apparatus itself and/or the memory card is locked easily by means of an intuitive operation by the user. This mobile terminal system (100) has a memory card (300) and a mobile terminal (200) in which the memory card (300) is inserted in a removable fashion. The mobile terminal (200) detects lengthy depression of a pressure section (202) pressed by the user by means of a long-depression detection section (204), and detects insertion of the memory card (300) inserted into a slot section (206) in a removable fashion by means of a card insertion/removal detection section (208). A locking execution section (218) locks or unlocks a function of at least one of the terminal (200) itself and/or the memory card (300). When the memory card (300) is removed from the slot section (206) during lengthy depression of the pressure section (202), the mobile terminal (200) locks or unlocks a function of at least one of the two using the locking execution section (218) via a terminal control section (220).