PURPOSE: To reduce the dead space for collection and to enhance the volumetric efficiency for collection, by equipping the inner barrel having the shape of circular truncated cone of which the upper end has a smaller diameter and the lower end has a larger diameter, inside the main body of the cold trap and, further, by making the passages for the functioning fluid in the front chamber and the rear chamber taper off.

CONSTITUTION: Inside the main body 1 of the cold trap having the inlet 2 and the outlet 3 for the functioning fluid, the inner barrel 17 having the shape of circular truncated cone is equipped. The functioning fluid from the inlet 2 passes through the front chamber 11 constituted of the inside wall 13, the outer surface of the inner barrel 17 and the vartical fins 18 and a greater part of the functioning fluid is solidified and collected at this chamber. The remaining functioning fluid changes direction by 180° at the lower end part of the inner barrel 17, flows into the rear chamber 12 to which the horizontal fins 4 are equipped and is solidified and collected completely in this chamber. The front chamber 11 and the reat chamber 12 are maintained respectively at an intermediately low temperature and a very low temperature with the refrigerant of intermediately low temperature and the refrigerant of very low temperature flowing the outer tube 20 and the inner tube 21