Multicomponent surfactant system, sodium dodecyl sulfate and butanol in an aqueous NaCl solution, which exhibits a closed-loop type reentrant phase separation, was investigated by light scattering experiments focusing on the double critical behaviors and the finite micellar size effect on the dynamic critical behavior. The loop size decreased with the decrease of NaCl concentration, and the double critical point appeared. Approaching the double critical point, the critical exponents nu for the long-range correlation length xi and gamma for the isothermal osmotic compressibility chi(T) determined by use of the spinodal divergency theory showed a crossover behavior from Fisher's renormalized Ising model values to the doubling of them. xi and chi(T) formed master curves as a function of epsilon(UL) = \(T-U-T)(T-L-T)\/TUTL, and had the effective critical exponents nu=0.73 and gamma=1.41 ascertaining the validity of Fisher's renormalized Ising model. Here, T-U and T-L are the upper and lower critical solution temperatures, respectively. Dynamic critical behaviors were well explained in a unified manner over the hydrodynamic and critical regions by the modified dynamical droplet model taking the finite micellar size into account, which assumes that the local fluctuations activated thermally behave as the physical clusters with a fractal dimension of d(f)=2.49 and a polydispersity exponent of tau=2.21. The evaluated monomer unit sizes are in good agreement with the micellar sizes obtained independently.