The purpose of this study is to estimate the energy response of a SKIN DOSE MONITOR (SDM model 104-101), which was developed to measure and assess medical exposure conveniently. The energy responses of pre-calibrated sensors were estimated by comparative measurements in the same calibration fields with sensors calibrated by Japan Quality Assurance Organization. The relative energy responses obtained for the precalibrated sensors agreed approximately with those of the calibrated sensors. The differences of the calibration factors in different calibration fields for the pre-calibrated sensors were 5 percent at the most in the range from 30keVto 40keVof effective energies. The sensor and coupling optical fiber of the SDM are faintly visible on a radiograph taken under ordinary operating conditions. The influence on diagnosis of this phenomenon is to be considered hereafter.