In this paper, we propose a method to improve the accuracy of depth map estimation from multi-view images using Neural Radiance Fields (NeRF). A depth map can be estimated from multi-view images using Multi-View Stereo (MVS), which can estimates the depths inside objects with high accuracy, while NeRF can estimate the depths at object boundaries with high accuracy. We consider using both advantages to improve the accuracy of depth map estimation from multi-view images and making NeRF as a refinement module. Through a set of experiments using a public MVS dataset, we demonstrate the effectiveness of the proposed method compared to conventional depth map estimation methods.