  We present the current-density functional theory for the superconductor
immersed in the magnetic field. The order parameter of the superconducting
state, transverse component of the paramagnetic current-density, and electron
density are chosen as basic variables that uniquely determine the equilibrium
properties of the system. In order to construct this theory, the development of
the approximate form of the exchange-correlation (xc) energy functional is
indispensable as well as the derivation of the effective single-particle
equation which makes it possible to reproduce the equilibrium densities
mentioned above. The rigorous expression of the xc-energy functional is derived
using the technique of the coupling-constant integration. Furthermore, the
approximate form of the xc energy functional is proposed such that the energy
gap resulting from the effective single-particle equation is consistent with
the attractive interaction energy of the system.
