We investigated the XBF-4B40 (4B40) thin bronchoscope, which has a 4.0-mm outer diameter and a 2.0-mm biopsy channel, and studied its impact on the diagnosis of lung carcinoma. We analyzed 30 peripheral lung carcinoma cases by performing bronchoscopic examination using the 4B40 and the type 200 videoscope and recorded the most distal bronchus level reached. In addition, transbronchial aspiration biopsy, forceps biopsy, or brushing was performed, and the diagnosis accuracy between the two instruments was determined. The mean of the most distal bronchus reached by the 4B40 and the type 200 videoscope was the 4.5th and the 3rd, respectively. The 4B40 reached significantly further into the distal bronchus than the type 200 videoscope (p<0.0001). Accuracy for lesions detected in the right segment 1 or left segment 1+2 using the 4B40 and the type 200 videoscope was significantly different (p<0.0001) at 90.0 and 0%, respectively. The new type of bronchoscope, XBF-4B40, is useful for peripheral pulmonary lesion diagnosis with diagnosis accuracy improvements in the right segment 1 or the left segment 1+2.