To decrease generation of magnetic noise greatly.

A cylinder of a first step cooling stage 21 of a GM refrigerating machine 2, a cylinder of a second step cooling stage 22, pressure resisting vessels of JT (Joule-Thompson) heat exchangers 31, 32, 33 of the first step, the second step, and a third step, a pressure resisting vessel of an adsorber 34, a JT valve 35, and at least one or preferably all of piping of a JT circuit 3, consist of non-magnetic substance.