Everybody, I'm sorry.
And, Thank you for many Information.
After having changed screen resolution to 800x600, I also tested.
At that time, the OK/Cancel button was not able to be seen.
However, it begins only to have seen it from the screen because the size of the
window was large.
and, I tested for 120dpi.
The result was the same after all.
If the window was resized, the button was able to be seen.
more, I examined it.
And, The problem has been understood.
When a window size was resized before a window was displayed.
(maybe, To screen resolution by the system because the size of the window is too large.
Or, by the system setting.)
A position and size of the Control do not seem to follow the resize of the window then when it fixed a position in an "Anchor" property of the Control.
I stopped using the "Anchor" property, and fixed the position by "Dock" property.
and, in "Load Event" of the Form, I added the next cord.
private Size displaySize()
int x = this.Width, y = this.Height;
foreach (Screen s in Screen.AllScreens)
x = Math.Min(x, s.WorkingArea.Width);
y = Math.Min(y, s.WorkingArea.Height);
x = Math.Max(x, this.MinimumSize.Width);
y = Math.Max(y, this.MinimumSize.Height);
return new Size(x, y);
This image is "800x600 120dpi", and the result of the display.
everybody, it troubled you.
Thank you and.