1. A cognitive function training unit for training cognitive function of a subject comprising: an eye-target showing means configured to show a movable eye-target on a display disposed in front of the subject's eye; an eye movement measuring means connected to an imaging device, the eye movement measuring means configured to measure at least one of a position and movement of the subject's eye by manipulating an image of the subject's eye obtained by said imaging device; and a judgment means configured to judge whether the subject can follow the eye-target based on at least one of a position and movement of the eye-target shown on said display and at least one of the position and the movement of the subject's eye measured by said eye movement measuring means, wherein said eye-target showing means is configured to show the eye-target repeatedly while changing at least one of the horizontal position, horizontal movement, amplitude and display time of the eye-target according to a judgment result of said judgment means, and wherein said judgment means is configured to judge that the subject cannot follow the eye-target when at least one of an eye position and an eye velocity of the subject measured by said eye movement measuring means is outside a predetermined variation range, and wherein said eye-target showing means is configured to change the position and/or the movement of the eye-target so that the subject can follow the eye-target, when said judgment means judges that the subject cannot follow the eye-target.