A referendum in a manner of direct democracy has been occasionally adopted in Japan for a political decision. However, it may not always maximize public interest, and it may thus lead failure. This referendum failure can easily emerge when those who insist a controversial policy, such as politicians who can benefit from the policy, use sophistry to justify the policy. This is because voters can not rationally judge the policy ouing to the sophistry. In this research we focus on politicians' remarks related to the referendum of "Osaka Metropolis Concept" of which voting day was 17th May, 2015 in Osaka City. We quantitatively analyzed remarks by 2 politicians, who are representative debaters in 2 major political parties in Twitter for a month (from 17th, April, 2015 to 17th, May, 2015), and remarks by them in a debate TV program casted in 12th, February, 2015. The result indicates that sophistry accounted for 33.9 % of the Twitter sentences and 48.0 % of the verbal sentences spoken by a politician who insisted the concept, whereas almost no sophistry (only 0.1 %) for the other politician. This result implies that there was risk that voters might not be able not rationally judge based on such frequent sophistry.