Plant cellulose is the most abundant organic compound on earth. Technologies for producing cellulose fiber or improving the enzymatic saccharification of cellulose hold the key to biomass applications. A technology for atomizing biomass without strong acid catalysis remains to be developed. The water jet is a well-known device used in machines (e.g., washing machines, cutters, and mills) that use high-pressure water. In this study, we examined whether a water jet system could be used to atomize crystalline cellulose, which comprises approximately 50% of plant biomass. The Star Burst System manufactured by Sugino Machine Limited (Sugino Machine; Toyama, Japan) is a unique atomization machine that uses a water jet to atomize materials and thereby places lower stress on the environment. After treatment with this system, the crystalline cellulose was converted into a gel-like form. High-angular annular dark-field scanning transmission electron microscopy showed that the cellulose fibers had been converted from a solid crystalline into a matrix of cellulose nanofibers. In addition, our results show that this system can improve the saccharification efficiency of cellulases by more than three-fold. Hence, the Star Burst System provides a new and mild pretreatment system for processing biomass materials.