The purpose of this paper is to examine the transition of the openness in auto-parts transaction, the tendency of carmakers to deal with new suppliers regardless of their transaction history, with transaction data of 169 auto-parts from 2005 to 2016. To achieve the purpose, I created six variables that are related to the openness. Contrary to former studies, three out of six variables supported that the openness was not progressing. The other supportive facts were about only after the big earthquake. From these results, I concluded the trend of the openness had already been changed in 2000s and discussed the background of this trend change.