Although patient exposure has been increasing in recent years, few institutions have dosimeters and are able to ascertain patients' exposure dose. Internationally, however, it is necessary to adopt safety levels for patient exposure doses, and guidance levels have been introduced. Therefore, the need for measurement in areas of x-ray diagnosis has been increasing. As a result, several societies concerned with radiation dose have been endeavoring to establish a calibration system of radiation measurement and a dosimeter calibration system, which are the basics of radiation protection. Ten regional centers for standardization of doses in x-ray diagnosis were established and have begun trials relating to dosimeter cross calibration. Our institution, as one of these centers, has instituted a trial. In this study, the cross-calibration field, the reliability of the cross-calibration skill of our regional center, and the standard uncertainty of cross calibration were investigated. As a consequence of the investigation, it was determined that our cross-calibration field follows the protocol of the Japanese Society of Radiological Technology, the difference between calibration factor/cross calibration factor obtained by JQA and our regional center is within 2.5%, and the expanded uncertainty of our cross calibration is about 7.2% (k=2).