A sample rotor is placed in a sample chamber inside an inner container. An air bearing type rotation mechanism blows a refrigerant gas (composed of a bearing gas and a driving gas) onto the sample rotor, to rotate the sample rotor and simultaneously cool the same. The refrigerant gas discharged from the air bearing type rotation mechanism is filled in an internal space (such as the sample chamber and a detection circuit chamber) of the inner container. An upper airtight chamber is formed between an outer container and the inner container. A lower airtight chamber is formed below a sealing bulkhead within a bottom unit. The upper and lower airtight chambers are in vacuum states to thereby function as vacuum insulation spaces for the internal space of the inner container.