A biodevice is in an elongated form and has a conductive layer and an insulating layer stacked on a side surface of a shaft member at the center. A cylindrical hollow section is formed through the device, being connected to the exterior at a front end and extending from this front end axially. An electrode section is formed on an inner surface. A sensing substance such as enzyme may be placed at the electrode section to detect a current value corresponding to the concentration or quantity of an object under test placed between a counter electrode and the biodevice.