To provide an X-ray detector, an apparatus and a method for X-ray measurement wherein X-rays can be detected with satisfactory accuracy without having to re-conduct, the calibration processing operation, even when the X-ray detector is replaced.

A data storage means which stores data on a calibration value used to calculate an X-ray measured value from a detection signal is installed at the X-ray detector 100, which detects the X-rays so as to output the detection signal. As the data storage means, a memory 105a inside a microcomputer 105 can be used. At the X-ray measuring apparatus 200, which calculates and outputs the X-ray measured value on the basis of the detection signal to be output from the X-ray detector 100, a microcomputer 204 which functions as a calibration-value-data readout means used to read out the data on the calibration value stored, in the memory 105a in the X-ray detector 100 and as a calculation means used to calculate the X-ray measured value, on the basis of the detection signal and on the basis of the data on the calibration value is installed.