1. A 3D imaging device for three-dimensionally imaging a subject and capturing a 3D image formed by a first viewing point image and a second viewing point image, the 3D imaging device comprising: an optical system configured to form an optical image of the subject; an imaging unit configured to generate the 3D image based on the formed optical image; a disparity detection unit configured to detect a disparity of the 3D image; a display parameter obtaining unit configured to obtain a display parameter associated with an environment in which the 3D image is viewed; a 3D perception determination unit configured to determine, during imaging for generating the 3D image, whether the generated 3D image will be easy to view three-dimensionally based on the detected disparity and the obtained display parameter; and a control unit configured to set a control mode for changing a positional relationship between the 3D imaging device and the subject when the 3D perception determination unit determines that the 3D image will be difficult to view three-dimensionally.