Neural Radiance Fields (NeRF) can be used for reconstructing scenes to render images at arbitrary viewpoints from a set of images, which requires numerous perspective images. The use of equirectangular images captured by a 360-degree camera makes it possible to render large-scale scenes with fewer input images since equirectangular images can capture the entire surrounding environment in a single shot. On the other hand, converting equirectangular images to perspective images is necessary for using them as input for NeRF. This conversion may introduce the strong distortion in the images, resulting in poor rendering quality. In this paper, we propose a preprocessing method that enables the use of equirectangular images as input to NeRF. We demonstrate the effectiveness of the proposed method through experiments on a public dataset.