This study is to acquire the confirmation data regarding the impressed current cathodic protection (ICCP) system by using the variable resistor for reinforced concrete specimens for improvement in under-protected area of reinforced concrete specimens. The ICCP system is one of the most promising corrosion protection methods. The Effect of ICCP system can be changed at diverse conditions. Particularly, temperature and relative humidity plays a crucial role in the CP effect. It was possible to confirm the performance of ICCP system by the use of variable resistor in different relative humidity and temperature conditions. The CP potential and current were measured by potentiostat, and 4 hour depolarization potentials were measured after disconnecting with anode for 4 hours. To enhance the effect of cathodic protection system, seawater was used as an electrolyte. Used anode for ICCP system was mixed metal oxide (MMO) titanium. From this study, it could be confirmed that the CP potential and current were highly influenced by temperature and relative humidity, and the CP effect in under-protected area has been improved by the ICCP system using the variable resistor.