  The phase transitions between the XY, the dimer and the Haldane phases of the
spin-1 bond-alternating XXZ chain are studied by the numerical diagonalization.
We determine the phase diagram at $T=0$ and also identify the universality
class with the level spectroscopy. We find that exactly on $\Delta=0$ there is
a Berezinskii-Kosterlitz-Thouless transition line which separates the XY and
the Haldane phase and there exists a multicritical point of the XY, the dimer
and the Haldane phases. We discuss that the critical properties of this model
is of the 2-D Ashkin-Teller type reflecting the hidden $Z_2\times Z_2$
symmetry.
