Lung cancer is categorized into two types; non-small cell lung cancer (NSCLC) with the 80~85% frequency and small cell lung cancer with the 15~20% frequency. Epidermal growth factor receptor (EGFR) is expressed on the surface of epidermal cells and has the tyrosine kinase activity. Overexpression of EGFR is found only in NSCLC and may lead to signal transduction system in cells by causing cell proliferation, tumor-induced neoangiogenesis (formation of new blood vessels) and transition induction. The EGFR tyrosine kinase inhibitor (TKI), gefinitib (Iressa, AstraZenca) or erlotinib (Tarceba, Roche), is effective to inhibit the growth of cancer cells and leads to death of cancer cells and suppression of new blood vessels in lung cancer tissue. Especially, some specific mutations in the ATP-binding domain of EGFR gene have strong positive correlation with the response rate of EGFR-TKIs. Furthermore, NSCLC patients with the EGFR mutations are reported to be more effective to EGFR-TKI and show prolonged survival rate of patients with lung cancer. Therefore, detection of the EGFR mutation is becoming an important prognostic biomarker for drug response, and efficient detection of the EGFR mutation is expected to be highly helpful for increase of survival rate of patients with lung cancer in targeted therapy.