1. A 3D imaging device for three-dimensionally imaging a subject and capturing a 3D image formed by a left eye image and a right eye image, the 3D imaging device comprising: an imaging unit configured to capture the 3D image; a distance information obtaining unit configured to obtain distance information indicating a distance from the 3D imaging device to the subject; a condition obtaining unit configured to obtain an imaging condition under which the 3D image has been captured and a display condition under which the 3D image will be displayed; an ideal disparity setting unit configured to set a disparity of the subject that will occur under the display condition as an ideal disparity, based on the obtained imaging condition and the obtained display condition; an actual disparity obtaining unit configured to detect a disparity of the subject occurring in the captured 3D image as an actual disparity; a disparity correction unit configured to perform disparity correction of the 3D image in a manner that the detected actual disparity is adjusted toward the set ideal disparity; a display information setting unit configured to set at least a viewing distance L and a base-line length S as display parameters associated with a viewing environment in which the 3D image is displayed, the viewing distance L being a distance between a display screen to display the 3D image thereon and a base-line that is a straight line connecting a left eye point and a right eye point in the viewing environment, the base-line length S being a distance between the left eye point and the right eye point in the viewing environment; wherein the condition obtaining unit sets a virtual screen at a position at which a distance to the subject matches the viewing distance L, and sets the imaging condition in a manner that a point of convergence is positioned on the virtual screen; when free positioning imaging is designated by the condition obtaining unit, and a placement position of the subject set by the condition obtaining unit is at a distance R 3 from the base-line, the disparity correction unit calculates a correction disparity Δx using the formula: Δx=x3−x2, where x3 is the ideal disparity and x2 is the actual disparity, and x3=S*(1−L/R 3 ), where S is the base-line length, and R 3 is the distance from the base line to the placement position, the base-line being a straight line including the left eye point and the right eye point, and L is the distance from the base-line to the display screen, and; the disparity correction unit performs disparity correction of the left eye image and the right eye image captured by the imaging unit by horizontally shifting the left eye image and the right eye image by an amount corresponding to the correction disparity Δx.