  By formulating open superstring field theory based on the small Hilbert space
of the superconformal ghost sector, an action for the Neveu-Schwarz sector with
an $A_\infty$ structure has recently been constructed. We transform this action
to the Wess-Zumino-Witten-like form and show that this theory is related to the
Berkovits formulation of open superstring field theory based on the large
Hilbert space by partial gauge fixing and field redefinition.
