Frequent replacement of a battery is avoided even if power consumption is large, and the structure is simplified and waterproofness is improved. Furthermore, cost reduction is achieved because driving components are selectable from components with variously different operating voltages. A hearing aid includes a secondary battery having a nominal voltage higher than a nominal voltage of an air battery, driving components driven by power at different voltages supplied from the secondary battery, and a transformation unit configured to output the charging power of the secondary battery at a voltage suitable for driving each driving component.