  In the vicinity of hole density, 1/8, La-based high-$T_{c}$ superconductors
exhibit long-range order of incommensurate antiferromagnetism (IC-AF).
Motivated by this observation, we explore the possible stabilization of IC-AF
ordering due to the existence of static charge density modulation (CDM). We use
Ginzburg-Landau free energy based on the mean field theory of the t-J model. It
is shown numerically that three kinds of CDM including a stripe pattern can
stabilize static IC-AF ordering. We also argue that such CDMs can cause the
saturation of the degree of incommensurability ($\eta$) as a function of hole
density for IC-AF fluctuation. In our framework a principal effect of
low-temperature tetragonal (LTT) structure is just to increase $\eta$ of IC-AF
slightly larger only for the stripe pattern.
