An apparatus for diagnosing a companion animal with radiation is provided. The apparatus includes a radiation irradiation unit configured to generate the radiation and irradiate the radiation toward a diagnosis object; a detector disposed to face the radiation irradiation unit and configured to detect the radiation irradiated from the radiation irradiation unit; a driving unit configured to adjust positions of the radiation irradiation unit and the detector; and a communication unit configured to communicate with an external device in a wireless manner. The driving unit adjusts the positions of the radiation irradiation unit and the detector such that the diagnosis object is located between the radiation irradiation unit and the detector, and the radiation irradiation unit irradiates the radiation toward the diagnosis object when the diagnosis object is located between the radiation irradiation unit and the detector.