  A degeneration of a singular curve on a toric surface, called a
tropicalization, was constructed by E. Shustin. He classified the degeneration
of 1-cuspidal curves using polyhedral complexes called tropical curves. In this
paper, we define a tropical version of a 1-tacnodal curve, that is, a curve
having exactly one singular point whose topological type is $A_3$, and by
applying the tropicalization method, we classify tropical curves which
correspond to 1-tacnodal curves.
