PURPOSE: To make the filling of active material operable uniformly into the tube, by inducting the active material into the tube in a manner of constructing an air flow coming from the supply port side of hopper toward the clad tube, with a supply tube of the active material engaged to the clad tube.

CONSTITUTION: Into a hole 9, provided in the top wall of a vessel 1, is up-down movably inserted an active material supply tube 10, the point end part of which is engaged to within a clad tube 1b. The above described supply tube 10 is connected to an elevator 13 for up-down moving said tube 10, and further connected to a bottom opening 15 of an active material supply hopper 14 through a fixed supply tube 10'. Subsequently, a suction exhaust operation is started with a vacuum pump 7 actuated further with a motor 20 rotating a stirrer 16 in the hopper 14. Exhaust actuation of the vaccum pump 7 causes an air flow to be generated flowing toward the clad tube, thus the stirred active material becomes dispersed flowing to be gradually deposited in the clad tube.