Hard X-ray (>15 keV) experiments for space astronomy require a detailed energy calibration in order to determine their true response matrix. To this end, we have built an X-ray facility, based on the use of a very stable X-ray generator plus an X-ray goniometer for crystal diffraction, that can provide collimated and monochromatic photons with energies in the range from about 15 keV to about 140 keV. We present a description of the facility and its performances. The facility has been already used to test samples of hard X-ray mirrors for space astronomy and it is being equipped to calibrate the high energy experiment PDS on board the X-ray astronomy satellite SAX.