To continuously carry out a product and waste material from an isotope separating device without cancelling vacuum in a vacuum vessel.

A differential exhaust system 20 is communicated with the bottom of a vacuum vessel (a) through a gate valve 10. In the differential exhaust system 20, plural sub-vacuum chambers 21 vertically forming a line, are communicated with each other and evacuated so that the lower the position of the sub-vacuum chamber 21 is, the more the degree of vacuum approaches atmospheric pressure. The product and waste material are introduced by a ribbed shooter part 40 and a water cooling shooter 41 to fall down and goes into the differential exhaust system 20 through the gate valve 10. The product and waste material move downward step by step through the sub-vacuum chambers 21 in the differential exhaust system 20 and falls down into a recovering vessel 50 from the lower end of the differential exhaust system 20. Even when the product and waste material move downward in the differential exhaust system 20, the degree of vacuum in each sub-vacuum chamber 21 is secured and the degree of vacuum in the vacuum vessel (a) is not lowered.