1. An apparatus with an orientation-following display, comprising: a display device having a screen that can be positioned in arbitrary postures including a reference posture relative to a space having a reference horizontal orientation, the screen having an xyz orthogonal coordinate system fixed to the screen, an x axis of the xyz orthogonal coordinate system being set parallel to a lateral direction in the space when the screen is positioned at the reference posture and a z axis of the xyz orthogonal coordinate system being perpendicular to the screen, the posture of the screen in the space being defined by z-x-z Euler angles α, β, and γ of the xyz orthogonal coordinate system, wherein the screen displays an image to enable recognition of the reference horizontal orientation of the space such that the reference horizontal orientation recognized in the screen coincides with the reference horizontal orientation of the space when the image is displayed on the screen at the reference posture; and a control device that derives α+β as an angle by which the image is rotated so that the reference horizontal orientation recognized from the image follows the reference horizontal orientation of the space when the image is displayed on the screen at arbitrary postures.