PROBLEM TO BE SOLVED: To provide a projection device capable of broadening a range in which a projection image based on a captured image of a subject is projected with high accuracy.SOLUTION: A projection device (20) includes an imaging unit (210), a projection unit (220), a controller (250), and an optical unit (201). The imaging unit images a subject to generate a captured image. The projection unit irradiates the subject with projection light representing a projection image based on the captured image. The controller controls the projection image on the basis of the captured image. The optical unit guides light so that an optical axis (J1) of incident light (310) incident on the imaging unit from the subject is coincident with an optical axis of projection light (320) irradiated from the projection unit onto the subject. An angle of view (θc) at which the imaging unit images on the basis of the incident light is coincident with an angle of view (θp) at which the projection unit irradiates the projection light, and an optical path length (Lc) of the incident light between the imaging unit and the optical unit is coincident with an optical path length (Lp) of the projection light between the projection unit and the optical unit coincide.SELECTED DRAWING: Figure 8B【課題】被写体の撮像画像に基づく投影画像が精度良く投影される範囲を広くする。【解決手段】投影装置（２０）は、撮像部（２１０）と、投影部（２２０）と、制御部（２５０）と、光学部（２０１）とを備える。撮像部は、被写体を撮像して撮像画像を生成する。投影部は、撮像画像に基づく投影画像を示す投影光を被写体上に照射する。制御部は、撮像画像に基づいて投影画像を制御する。光学部は、被写体から撮像部に入射する入射光（３１０）の光軸（Ｊ１）と、投影部から被写体上に照射される投影光（３２０）の光軸とが一致するように導光する。入射光に基づき撮像部が撮像する画角（θｃ）と、投影部が投影光を照射する画角（θｐ）とが一致し、撮像部と光学部間の入射光の光路長（Ｌｃ）と、投影部と光学部間の投影光の光路長（Ｌｐ）とが一致している。【選択図】図８Ｂ
