A portable device for displaying charge information has a transmission unit for wirelessly transmitting a signal, requesting charge information on a battery, to a controller provided with a unit for detecting a remaining amount of a battery, a reception unit for wirelessly receiving the charge information from the controller, a storage unit for storing charge information received by the reception unit, a display unit for displaying charge information stored into the storage unit, and a charge prediction information calculating unit for calculating prediction information regarding a state-of-charge of the battery based upon charge information stored in the storage unit in the case of the reception unit being unable to receive charge information from the controller after transmitting a signal requesting charge information from the transmission unit. The prediction information calculated by the charge prediction information calculating unit is displayed in the display unit.