A mobile terminal device communicates with a base station in one of a power-saving state in which consumption of power supplied from a built-in power supply is suppressed and a normal state in which the consumption of power supplied from the built-in power supply is not suppressed. The mobile terminal device includes a base station detecting unit that detects a maximum-power received-wave base station of which a received-wave power is maximum, a base-station-change detecting unit that detects whether the maximum-power received-wave base station detected by the base station detecting unit is changed, and a power-saving-state transition control unit that controls transition to the power-saving state when the change of the maximum-power received-wave base station is not detected by the base-station-change detecting unit in a predetermined time in the normal state.