  We study the S-matrix elements of the gauge invariant operators corresponding
to on-shell closed strings, in open string field theory. In particular, we
calculate the tree level S-matrix element of two ${\it arbitrary}$ closed
strings, and the S-matrix element of one closed string and two open strings. By
mapping the world-sheet of these amplitudes to the upper half $z$-plane, and by
evaluating explicitly the correlators in the ghost part, we show that these
S-matrix elements are ${\it exactly}$ identical to the corresponding disk level
S-matrix elements in perturbative string theory.
