An electric device according to the present invention includes: a first power source which supplies electric power to a predetermined load unit; a second power source which supplies electric power from an outside power source to the load unit; a switching unit which switches the first power source and the second power source which supply electric power to the predetermined load unit; a time measuring unit which measures the time; a voltage measuring unit which measures terminal voltage of the first power source; a storage unit which stores the terminal voltage of the first power source measured by the measuring unit and the time when the terminal voltage of the first power source is measured based on the time measuring unit; a time change rate calculating unit which calculates a time change rate of the terminal voltage of the first power source stored in the storage unit; and an informing unit which performs informing operation with respect to a residual capacity of the first power source in accordance with the time change rate of the terminal voltage of the first power source calculated by the time change rate calculating unit.