PURPOSE: To prevent that a measuring probe is affected by the mechanical vibration and magnetical vibration caused by a freezer though the freezer is used in order to cool the measuring probe of an SQUID fluxmeter to hold the same to extremely low temp.

CONSTITUTION: The main body 22 of a freezer 9 is arranged so as to be spaced apart from a vacuum heat insulating cooling container 2 having a measuring probe 1 received therein. The cooling head 18 of the freezer 9 is drawn out of the freezer main body 22 by a flexible pipeline 24 and only the cooling head 18 is arranged in the vacuum heat insulating cooling container 2.