A subject information acquisition apparatus, comprises: a signal generation unit configured to generate a high-frequency signal corresponding to each of the frequencies; an acquisition unit configured to acquire a plurality of detection signals based on at least one of a reflection signal and a transmission signal; a signal selection unit configured to select at least one detection signal from the plurality of detection signals based on an index value of the plurality of detection signals; a coupling amount detecting unit configured to detect a coupling amount of near-field coupling due to an electric field between the antenna and the subject based on a detection signal; and a displacement detecting unit configured to generate a displacement signal indicating a displacement of the subject based on the coupling amount.