  We report on the experimental results of interlayer magnetoresistance in
multilayer massless Dirac fermion system $\alpha$-(BEDT-TTF)$_2$I$_3$ under
hydrostatic pressure and its interpretation. We succeeded in detecting the
zero-mode Landau level (n=0 Landau level) that is epected to appear at the
contact points of Dirac cones in the magnetic field normal to the
two-dimensional plane. The characteristic feature of zero-mode Landau carriers
including the Zeeman effect is clearly seen in the interlayer
magnetoresistance.
