PURPOSE: To measure radioactivity of an object having arbitrary shape while shortening the measuring time by performing local contamination measurement of the radioactivity intensity of a containing object and dissolving an object lower than an allowable limit into fluoboric acid thereby converting the object into a measurable form.

CONSTITUTION: Entire surface of an object 10 to be contaminated is sensed by means of a contact sensor and specific radioactivity is determined by roughly performing local measurement 11 of the intensity of radioactivity for a sample obtained by boring a material. All objects lower than a limit value of 20n Ci/g, for example, are immersed into fluoboric acid (HBF4) 12 and dissolved perfectly thus bringing the object into a first measurable form. The entire solution is then stirred and homogenized before the substance is separated through precipitation or electrolysis. Radioactivity is then measured for a metal deposited on the cathode through electrolysis and when the radioactivity is lower than a limit level, it is used as scrap 14 with no limitation. HBF4 serving as an electrolyte is circulated for reuse and regenerated 15 when the radioactivity has increased. Separated deposit is cemented 16 and a surface contaminated object exceeding the limit level is decontaminated 17 using HBF4.