Twitter is a famous social networking service and has received attention recently.Twitter user have increased rapidly, and many users exchange information. When 2011 Tohokuearthquake and tsunami happened, people were able to obtain information from social networkingservice. Though Twitter played the important role, one of the problem of Twitter, a false rumordiffusion, was pointed out. In this research, we focus on a false rumor diffusion. We propose ainformation diffusion model based on SIR model, and discuss how to prevent a false rumor diffusion.