This invention has one object to provide a method of collecting calibration data in radiation tomography apparatus that allows reliable collection of calibration data with a wide detector ring. In order to achieve this purpose, in the method of collecting calibration data in radiation tomography apparatus according to this invention, the number of coincidence events is obtained while the phantom that emits annihilation gamma-ray pairs moves as to pass through an inner hole of the detector ring. Such configuration dose not need the phantom having a width equal or larger than the detector ring, and may realize reliable collection of calibration data. Moreover, it may be considered that annihilation gamma-ray pairs have been emitted in uniform property without depending on positions of the detector ring. As a result, calibration data that is more suitable for removal of a image artifact may be obtained.