The Courant-Friedrichs-Lewy condition (The CFL condition) is
appeared in the analysis of the finite difference method
applied to linear hyperbolic partial differential equations.
We give a remark on the CFL condition from a view point of
stability, and we give some numerical experiments
which show instability of numerical solutions even under the
CFL condition. We give a mathematical model for rounding errors
in order to explain the instability.