  We calculate one-loop 2-point tachyon amplitudes in unoriented open-closed
string field theory, and determine all the coupling constants of the
interaction vertices in the theory. It is shown that the planar, nonplanar and
nonorientable amplitudes are all reproduced correctly, and nontrivial
consistencies between the determined coupling constants are observed. The
necessity for the gauge group to be SO(2^{13}=8192) is also reconfirmed.
