  The analytic method for deriving the equation of state of a cell fluid model
in the region above the critical temperature ($T \geqslant T_\text{c}$) is
elaborated using the renormalization group transformation in the collective
variables set. Mathematical description with allowance for non-Gaussian
fluctuations of the order parameter is performed in the vicinity of the
critical point on the basis of the $\rho^4$ model. The proposed method of
calculation of the grand partition function allows one to obtain the equation
for the critical temperature of the fluid model in addition to universal
quantities such as critical exponents of the correlation length. The isothermal
compressibility is plotted as a function of density. The line of extrema of the
compressibility in the supercritical region is also represented.
