[en] A portable RI X-ray fluorescence spectrometer having a weight of 1800 g was constructed by using a radiation annular source (²⁴¹Am sealed up with ceramics, 1.85 MBq), a small Si-PIN photodiode X-ray detector mounted on a Peltier cooling device, an amplifier and a pocket-type multi-channel pulse-height analyzer. It could also be applied to a non-destructive analysis of the blue colorant in the original Japanese votive picture 'Rashoumon-zu', offered to shrine in 1682. Consequently, it was clarified that the blue colorant (X) was 'Smalt' containing Ga, Fe, Co, Ni and As as major elements. (author)