PURPOSE: To improve greatly the stability of acquisition efficiency and to realize a high-speed, high-precision analytic sample, by controlling the velocity of serial feed water flow in a filter and a column, and detecting the valve point of the filter.

CONSTITUTION: A pretreating device is provided with piping 7A, and a low pressure system 21 and a high pressure system 25 on the passage of the piping 7A, and for feedback control, a flow meter 20 is provided at the waste water side of an ion exchange resin column 6 through a valve 40. In a waste water tank 22, a level gauge 23 for valve point detection is provided. Through this constitution, while the velocity of serial feed water in the filter and column is controlled, the valve point of the filter is detected to improve the stability of acquisition efficiency greatly, thereby realizing the high-speed, high-precision radioactive analytic sample.