Extended supersymmetric σ-model is given, standing on the SO(2N+1) Lie algebra of fermion operators composed of annihilation-creation operators and pair operators. Canonical transformation, the extension of the SO(2N ) Bogoliubov transformation to the SO(2N + 1) group, is introduced. Embedding the SO(2N + 1) group into an SO(2N +2) group and using SO(2N+2) U (N+1) coset variables, we investigate a new aspect of the supersymmetric σ-model on the Kähler manifold of the symmetric space SO(2N+2) U (N+1) . We construct a Killing potential which is just the extension of the Killing potential in the SO(2N ) U (N ) coset space given by van Holten et al. to that in the SO(2N+2) U (N+1) coset space. To our great surprise, the Killing potential is equivalent with the generalized density matrix. Its diagonal-block matrix is related to a reduced scalar potential with a Fayet-Ilipoulos term. The reduced scalar potential is optimized in order to see the behaviour of the vacuum expectation value of the σ-model fields and a proper solution for one of the SO(2N + 1) group parameters is obtained. We give bosonization of the SO(2N+2) Lie operators, vacuum functions and differential forms for their bosons expressed in terms of the SO(2N +2) U (N +1) coset variables, a U (1) phase and the corresponding Kähler potential. * A preliminary version of this work has been presented by S. Nishiyama at the YITP workshop YITP-W-07-05 on String Theory and Quantum Field Theory held at Kinki University