PROBLEM TO BE SOLVED: To provide an interface inspection method of a composite structure capable of efficiently performing inspection of an interface state of a concrete structure while improving inspection accuracy.SOLUTION: The interface inspection method includes: a step (S31) to acquire a signal waveform by giving an impact to a first abnormal sound generating part which is determined in a step to determine the interface state in the composite structure on the basis of acoustic echo in the composite structure; a step (S32) to acquire an envelope by performing envelope detection on the acquired signal waveform; steps (S33, S34) to determine a state of water strapped in a space on the basis of an attenuation coefficient representing an attenuation characteristic in an attenuation curve; a step (S38) to acquire signal waveform by allowing a supersonic wave to propagate in a transmitter probe in the composite structure to a second abnormal sound generating part; a step (S39) to acquire an amplitude characteri
