  A new method of determining Primary Cosmic Ray mass composition is proposed.
The method is based on quasi-localization of the integral equation for the
Extensive Air Showers spectrum versus the total number of high energy muons
($E_\mu \geqslant 235$ GeV) and an expansion of the experimentally measured
spectrum in spectra of five group of primary nuclei. The cosmic ray mass
composition is established in the energy region $10^{14}-10^{16}$ eV. In the
region $10^{15}-10^{16}$ eV our analysis points to a lightening of the mass
composition from $p+\alpha \simeq 0.54,\ \langle \ln A \rangle \simeq 1.97$ to
$p+\alpha \simeq 0.69,\ \langle \ln A \rangle\simeq 1.56$.
