  For the two dimensional dilaton-coupled quantum gravity model, we give the
local black hole mass, which is an analogue of what was first introduced by
Fischler, Morgan and Polchinski in the four dimensional gravitational systems.
We analyze the original CGHS model with this local mass and find that the local
mass is decreasing in the future direction on the matter shock-wave line, while
it stays constant at past null infinity.
