The single electron transistor was fabricated by quite a new fabrication process using scanning tunneling microscopy, The single electron transistor operates at room temperature showing a clear Coulomb staircase of 150 mV periods. The tip of the scanning tunneling microscope was used as a cathode, and the surface of the Ti layer was oxidized to form a narrow oxidized Ti line. Using this oxidized Ti line, the island region of the single electron transistor was fabricated. The electrical property of the oxidized Ti line was also examined in detail.