A novel simple-shield thermocouple that is capable of radiation correction in fire environments and that has a simpler structure and greater convenience than conventional aspirated thermocouples was proposed. The measurement errors of bare-bead, double-shield aspirated, and simple-shield thermocouples were then compared in a simulated fire environment. In addition, a fire experiment using wood cribs was performed in order to verify the measurement performance of the proposed simple-shield thermocouple in a real fire environment using a one-third-scale ISO 9705 room. The simple-shield thermocouple produced fairly accurate temperatures that fell within 5% of the actual gas temperature in the simulated fire environment. In addition, variations in the surface emissivity and the installation angle of the simple-shield thermocouple in the real fire environment further reduced the measurement error. With a radiant heat flux of 20 kW/m2, it was confirmed that the bare-bead thermocouple had a relative measurement error of up to 80% compared to the aspirated thermocouple, while the proposed simple-shield thermocouple was capable of measuring the temperature within a relative error of around 15% compared to the aspirated thermocouple.