[en] In the apparatus for mass spectroscopic study of the vaporization of Pu fuel material, the ionization room of a quadopole mass spectroscope is about 10 cm above the knudsen cell, which is heated by a pair of W coil resistance heaters. Ion pumps are used to evacuate the chamber including the cell, and pressure in the chamber is 10^-8 -- 10^-6 mmHg depending on temperature of the cell (room temperature to 1800⁰C). The apparatus except a main ion pump and two sorption pumps is in a Pu glove box, 100 x 225 x 110 cm. To examine performance of the apparatus, the vaporization of Ag was measured. A log IT vs. 1/T curve shows slope changes near the melting point of Ag: ΔH⁰sub(vap) = 60.1 Kcal.mole^-1 and ΔH⁰sub(sub) = 66.8 Kcal.mole^-1 are in agreement with those in the literature. (auth.)