This paper deals with high-speed all-in-focus image reconstruction by merging multiple differently focused images. Previously, we proposed a method of generating an all-in-focus image from multi-focus imaging sequences based on spatial frequency analysis using three-dimensional FFT. In this paper, first, we combine the sequence into a two-dimensional image having fine quantization step size. Then, just by applying a certain convolution using two-dimensional FFT to the image, we realize high-speed reconstruction of all-in-focus images robustly. Some simulations utilizing synthetic images are shown and conditions achieving the good quality of reconstructed images are discussed. We also show experimental results of high-speed all-in-focus image reconstruction compared with those of the previous method by using real images.