A device for testing a tyre (2) for representing tomographical images of sections of a casing of the tyre includes a source (11) of ionizing radiation arranged outside the tyre (2) and a detector (12) for receiving the radiation. The detector (12) is situated opposite the source (11) with respect to at least one section of the casing. The axis (X-X) of the tyre runs parallel to a sectional plane (P) passing through the focus (F) of the source (11) and the detector (12). The tyre and the source-detector assembly are moved with rotational motion relative to one another about an axis of rotation (Z-Z) perpendicular to the sectional plane (P), according to a predetermined angular excursion range. The detector (12) is disposed in a central internal zone (20) of the tyre (2) during the testing cycle.