A geometrical approach in string field theory

String theory is believed to be a consistent quantum theory which unifies gravity and other forces and matter fields. Since, according to Einstein, gravity tells us the geometry of space-time, string theory should be formulated in a way that is independent of the background geometry. An attempt is made to analyze one of the proposals on geometric formulation of string theory. Geometric quantization is explained in detail. The loop space of background geometry is studied also to see whether we get consistent string theories. An extension to superstring is given, showing that the phase space of open superstring is also a Kaehler manifold. The geometrical meaning of ghosts of string theory is studied to construct a string field theory where ghost fields, c(σ) and string coordinates xμ(σ) stand on a same footing. The BRST formalism for the open string field is rederived, while the Bowick and Rajeev proposal is modified. Namely, it is conjectured that the closed string field is a Kaehler potential of the extended loop space, the set of maps, S1 → (xμ, ρ), where ρ is the conformal factor of a string worldsheet