We study tachyon condensation in the noncommutative open string (NCOS) theory in the boundary string theory (BSFT) formalism. We explicitly construct an effective action for a tachyon including a gauge field. Based on our action, it is shown that there exists an electric flux tube at the vacuum of the tachyon. Its tension and positiveness suggest that after tachyon condensation we have a non-relativistic closed string (NRCS) proposed by Gomis and Ooguri. ©2002 American Institute of Physics.