  We report the observation of nonlinear anomalous Hall effect (NLAHE) in the
multilayered organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ in the charge order
(CO) insulating phase just under the critical pressure for transition into
two-dimensional (2D) massless Dirac fermion (DF) phase. We successfully
extracted the finite nonlinear Hall voltage proportional to square current at
zero magnetic field. The observed NLAHE features, current direction dependence
and correlation with CO, are consistent with the previous estimation assuming
2D massive DF with a pair of tilted Dirac cones. This is the first observation
of topological transport in organic conductors, and also the first example of
NLAHE in the electronic phase with spontaneous symmetry breaking.
