  A detailed electronic phase diagram of perovskite-type oxides
Sr$_{1-x}$La$_x$FeO$_3$ $(0\leq x \leq 0.5)$ was established by synchrotron
X-ray diffraction, magnetization, and transport measurements for
polycrystalline samples synthesized by a high-pressure technique. Among three
kinds of helimagnetic phases in SrFeO$_3$ at zero field, two of them showing
multiple-${\it q}$ helimagnetic spin textures tend to rapidly disappear in
cubic symmetry upon the La substitution with $x$ less than 0.1, which
accompanies the loss of metallic nature. On the other hand, the third
helimagnetic phase apparently remains robustly in Sr$_{1-x}$La$_x$FeO$_3$ with
$x$ higher than 0.1, followed by merging to the spin/charge ordered phase with
$x\sim 1/3$. We propose an important role of itinerant ligand holes on the
emergence of multiple-${\it q}$ states and a possible link between the third
(putative single-${\it q}$) helimagnetic phase in SrFeO$_3$ and the spin/charge
ordered phase in Sr$_{2/3}$La$_{1/3}$FeO$_3$.
