c:\php is my *.php store directory.
There are two options to change default htdoc folder.
DocumentRoot "C:/PHP"
<Directory "C:/PHP">
I did not set the second one.
It seems you pointed me to the right direction.
I did not remember there are two options to change htdoc folder.
So it is solved now.
When index.html missing, I can see and choose any file in folder to run. I do not use index.html on my PC server(local)