We investigate an alternative quantization of R-NS string theory. In the
alternative quantization, we define the distinct vacuum for the left-moving
mode and the right-moving mode by exchanging the role of creation operators and
annihilation operators in the left-moving sector. The resulting string theory
has only a finite number of propagating degrees of freedom. We show that an
appropriate choice of the GSO projection makes the theory tachyon free. The
spectrum coincides with the massless sector of type IIA or type IIB superstring
theory without any massive excitations.