To provide a protection tube for a thermocouple capable of maintaining air-tight sealability for a connection part even when carrying out 1100°C or more of high-temperature heat treatment in a horizontal furnace using a heat-treating tube, and a temperature measuring instrument using the same.

In this protection tube for the thermocouple provided at least with an insertion part inserted into the heat-treating tube equipped to the horizontal furnace, and the connection part for air-tight connection to the heat-treating tube via a sealant, at least the connection part comprises quartz, and the insertion part comprises a material having heat resistance higher than that of quartz, and the temperature measuring instrument using the protection tube is also provided.