Thanks to comments from the front thread, I downloaded EzDome and got a hdr background.

By the way, only a part of the background comes out. I want to see the whole background.

so, i changed u and v Scale in the advanced setting, The uv size was not changed.

How do I make it look like a sample?

And I don't know, When I register with the ezdome library, I saved both Inner and Out images to the same file. Is this correct?

Keep in mind, you are projecting an image on a 360-degree dome which makes it impossible to view as a single panoramic scene. Your best alternative is to place the HDRI on a Hi-Res flat plane and position it behind your actual scene. However, you need to match the x-/y-scale to the image in pixels or you will introduce distortions and resolution issues. You will, most likely, need to use a .jpg or .png image for the flat plane, allowing the HDRI to provide the environmental lighting to the scene. Remember, any flat image generated from a panorama HDRI is a 360-degree map stretched over a flat projection. Sometimes the image looks right or may appear like the image below which just doesn't look right on a plane.