Single-walled carbon nanotubes (SWNTs) were produced with a high content using a newly designed chamber. The feature of the chamber is that the DC arc-generation section is connected horizontally to the heater section with the filtering zone. Soot with a high content of SWNTs is selectively trapped on the sample collector located in the heater section, utilizing the flight distance of arc-produced components in the filtering zone under controlled gas flow. Further SW-NT growth was demonstrated during in situ heat treatment in the heater section. The G/D value, which is obtained from Raman spectroscopy and is a good index of SWNT content, increased from 4.3 to 25.9.