  We present a construction of open-closed string field theory based on disc
and RP2 geometries. Finding an appropriate BRS operator in the case of the RP2
geometry, we generalize the background independent open string field theory (or
boundary string field theory) of Witten on a unit disc. The coupling constant
flow at the closed string side is driven by the scalar operator inserted at the
nontrivial loop of RP2. We discuss the off-shell extension of the
boundary/crosscap states. Our construction provides an interpolation of
orientifold planes of various dimensions as well as that of D-branes.
