Equations are derived for the gasdynamics of a dense plasma confined by a multiple-mirror magnetic field. The limiting cases of large and small mean free paths have been analyzed earlier: λ ≪ ι0 and λ ≫ ιk, where ι is the length of an individual mirror machine, ι0 is the size of the mirror, and k is the mirror ratio. The present work is devoted to a study of the intermediate range of mean free paths ι0 ≪ λ ≪ ιk. It is shown that in this region of the parameters the process of expansion of the plasma has a diffusional nature, and the coefficients of transfer of the plasma along the magnetic field are calculated.