PURPOSE: To provide the image diagnostic device which eliminates the trouble of operations due to an operator by displaying a comment in a diagnostic image before switching at a certain position corresponding to the displaced part (new coordinate) of the diagnostic image after switching.

CONSTITUTION: An image corresponding comment redisplay part 7 recognizes the coordinate of an image displayed corresponding to information from an image display state switching part 5 and the coordinate of an image displayed corresponding to information from a comment display part 6, and the coordinate of the switched image is inputted by operating the image display state switching part 5. Then, the component of displacement between the coordinate and the coordinate of the image before switching is calculated, the coordinate of the comment displayed in the image before switching is transformed corresponding to the displaced component, the comment is displayed in the transformed coordinate, and the display of the comment displayed up to the moment is erased. Therefore, since the respective kinds of control are performed by a main controller 8 and a console 9, the trouble of operations due to the operator can be eliminated.