The purpose of the present invention is to provide a video-tracking-information detection device that is capable of acquiring information for causing a central portion of a video to track the line of sight of a user. A video-tracking-information detection device (10) according to the present invention is provided with: a video display system (100) including a video-light projection unit (110) that projects video light and a transmissive reflection member (120) that reflects a portion of the video light projected from the video-light projection unit (110) toward an eyeball (1) and that allows the other portion to be transmitted therethrough; and a line-of-sight detection system (200) including at least one invisible light source (211), a diffraction optical element (212c) provided integrally with the transmissive reflection member (120) and including a reflective diffraction part (212c1) that reflectively diffracts invisible light from the invisible light source (211) toward the eyeball (1), and a light receiving element (220a) that receives the invisible light reflected by the eyeball (1) and reflectively diffracted by the reflective diffraction part (212c1). A portion (120a) of the transmissive reflection member (120), irradiated with a central portion of the video light, overlaps the reflective diffraction part (212c1) when viewed from the thickness direction of the transmissive reflection member (120).
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