We have evaluated the absorption dose by simulation in a phantom irradiated by the X‐ray from the 6MeV electron synchrotron MIRRORCLE‐6X. Comparison with the dose by the X‐ray from a 100keV X‐ray tube was made. It shows that the averaged dose integrated over the phantom to make one flame of the X‐ray image in the case of MIRRORCLE‐6X is much smaller than that in the case of the X‐ray. We have also measured the dose using MIRRORCLE‐6X under the various conditions. We could confirmed this results experimentally by observing dose at the surface, although it was slightly higher than expected. © 2004 American Institute of Physics