To thermally shield an isothermal region by inserting an adapter between a thermocouple probe and a multimeter (DMM), providing a sensor and a probe receptacle in the isothermal region, and providing a high-thermal resistance region between the isothermal region and an input terminal.

A DMM adapter 40 is provided with plugs T, P adaptable to the jacks V, C of a DMM 10. The contact regions 31, 32 of the plug T are connected to the connector receptacle 37 of a thermocouple probe 50 and the output terminal Ts of a temperature sensor 36 respectively, the contact regions 33, 34 of the plug P are connected to the (+), (-) input terminals of the temperature sensor 36 respectively, and the receptacle 38 of the thermocouple probe 50 is connected to the contact region 34 of the plug P. The temperature sensor 36 and the receptacles 37, 38 are thermally connected to an isothermal region 35, and the isothermal region 35 and a reference thermocouple are thermally connected when the connector terminals 51, 52 of the thermocouple probe 50 are mated with the receptacles 37, 38, thereby the isothermal region 35 is thermally shielded from the contact regions 31, 32 and the contact regions 33, 34 by a high-thermal resistance region 39 to the utmost.