Abstract: In a battery power supply apparatus for low-noise measurement systems or ultra high-sensitivity sensor elements (ultra-sensitive light or microwave sensors, or SQUID, SIS/SNS or other Josephson effect devices, etc.), the power supply device that supplies power to the outside and the control device that controls the power supply device perform bidirectional communications by means of an optical communications circuit, and thus it is possible to prevent noise arising in the control device from reaching the power supply device. In addition, it is possible to prevent the introduction of noise from the optical communications circuit into the power supply device within a shield case. Accordingly, it is possible to control the operation of the power supply device enclosed within the shield case from the control device outside of the shield case without having external noise affecting the power supply device.