A hearing aid comprising: a secondary battery having a nominal voltage higher than a nominal voltage of 1.4 V of an air battery; at least one driving component driven by power supplied from the secondary battery; a power-receiving module configured to receive power from the outside of the hearing aid in a contactless manner; a first processing circuit including: a charging unit configured to supply DC power at a predetermined voltage to the secondary battery; and a rectifier configured to output DC power to the charging unit by rectifying AC power supplied to the power-receiving module; and a second processing circuit including: a transformation unit configured to output the charging power of the secondary battery to the at least one driving component, at a voltage suitable for driving the at least one driving component; a detection unit configured to detect that the first processing circuit is in an operating state; and a switching controller configured to switch the transformation unit from an operating state to a stopped state only when the detection unit detects that the first processing circuit is in the operating state, wherein the at least one driving component is driven at a voltage of 1.4 V, the transformation unit is a voltage dropping circuit configured to decrease voltage to be lower than the terminal voltage of the secondary battery, the voltage dropping circuit is a switching regulator, the first processing circuit and the second processing circuit are provided on a single-chip integrated circuit substrate, and the second processing circuit is disposed at a position which causes the first processing circuit to malfunction from noises generated by the second processing circuit in accordance with signal processing. a secondary battery having a nominal voltage higher than a nominal voltage of 1.4 V of an air battery; at least one driving component driven by power supplied from the secondary battery; a power-receiving module configured to receive power from the outside of the hearing aid in a contactless manner; a first processing circuit including: a charging unit configured to supply DC power at a predetermined voltage to the secondary battery; and a rectifier configured to output DC power to the charging unit by rectifying AC power supplied to the power-receiving module; and a charging unit configured to supply DC power at a predetermined voltage to the secondary battery; and a rectifier configured to output DC power to the charging unit by rectifying AC power supplied to the power-receiving module; and a second processing circuit including: a transformation unit configured to output the charging power of the secondary battery to the at least one driving component, at a voltage suitable for driving the at least one driving component; a detection unit configured to detect that the first processing circuit is in an operating state; and a switching controller configured to switch the transformation unit from an operating state to a stopped state only when the detection unit detects that the first processing circuit is in the operating state, wherein the at least one driving component is driven at a voltage of 1.4 V, the transformation unit is a voltage dropping circuit configured to decrease voltage to be lower than the terminal voltage of the secondary battery, the voltage dropping circuit is a switching regulator, the first processing circuit and the second processing circuit are provided on a single-chip integrated circuit substrate, and the second processing circuit is disposed at a position which causes the first processing circuit to malfunction from noises generated by the second processing circuit in accordance with signal processing. a transformation unit configured to output the charging power of the secondary battery to the at least one driving component, at a voltage suitable for driving the at least one driving component; a detection unit configured to detect that the first processing circuit is in an operating state; and a switching controller configured to switch the transformation unit from an operating state to a stopped state only when the detection unit detects that the first processing circuit is in the operating state, wherein the at least one driving component is driven at a voltage of 1.4 V, the transformation unit is a voltage dropping circuit configured to decrease voltage to be lower than the terminal voltage of the secondary battery, the voltage dropping circuit is a switching regulator, the first processing circuit and the second processing circuit are provided on a single-chip integrated circuit substrate, and the second processing circuit is disposed at a position which causes the first processing circuit to malfunction from noises generated by the second processing circuit in accordance with signal processing.