An apparatus for introduction into a test body includes a functional portion for obtaining information on an inside of a test body a power source for supplying power for driving the functional portion and an enclosed container for accommodating the functional portion and the power source. A cross-sectional shape orthogonal to a longitudinal direction of the enclosed container is an elliptical shape to make an outer shape small to alleviate a burden on a test subject during introduction into a body by swallowing or the like for test.
