Amyloid fibrils are self-assemblies of proteins with an ordered cross- " architecture and are associated with serious disorders. Amyloid fibrillation is similar to the crystallization of solutes from a supersaturated solution. We found that ultrasonication triggers the spontaneous formation of fibrils in solutions of monomeric amyloidogenic proteins. Cavitation microbubbles are likely to play a key role in effectively converting the metastable state of supersaturation to the labile state, leading to spontaneous fibrillation. With a newly constructed instrument, a HANdai Amyloid Burst Inducer (HANABI), the ultrasonication-forced fibrillation of proteins can be automatically and rapidly analyzed. The results with hen eggwhite lysozyme suggested that the large fluctuation observed in the lag time for amyloid fibrillation originated from a process associated with a common amyloidogenic intermediate. The HANABI system will also be useful for studying the mechanism of crystallization of proteins because proteins form crystals by the same mechanism as amyloid fibrils under supersaturation.