In order to produce a cheap and stable X-ray generator system for calibration of dosimeters used in mammographic field, a dummy source of mammographic X-ray was developed using a tungsten (W) target X-ray tube and a molybdenum (Mo) filter. The photon fluence spectra of mammographic equipment were calculated using Birch’s formula and aluminum (Al) attenuation curves were derived. The Al attenuation curves of X-rays from W target with Mo filter of various thicknesses were similarly obtained. Comparing the similarities of attenuation curves, the best fit Mo filter thickness was chosen. Consequently, a 0.04 mm thick Mo plus a 4 mm thick poly-methylmethacrylate filter were chosen to be added to W target industrial X-ray tube. The similarity of Al attenuation curves were verified by ionization chamber measurements.