  The constraint structure of 2D-gravity with the Weyl and area-preserving
diffeomorphism invariances is analysed in the ADM formulation. It is found that
when the area-preserving diffeomorphism constraints are kept, the usual
conformal gauge does not exist, whereas there is the possibility to choose the
so-called ``quasi-light-cone'' gauge, in which besides the area-preserving
diffeomorphism invariance, the reduced Lagrangian also possesses the SL(2,R)
residual symmetry. The string-like approach is applied to quantise this model,
but a fictitious non-zero central charge in the Virasoro algebra appears. When
a set of gauge-independent SL(2,R) current-like fields is introduced instead of
the string-like variables, a consistent quantum theory is obtained.
