The present study was conducted with students of Yamaguchi Elementary School attached to the Faculty of Education, Yamaguchi University, with the purpose of fostering critical thinking attitudes based on an infusion approach. The aim of this study was to understand that thinking based on evidence is useful in solving problems in daily life. The results of the questionnaire survey showed a significant increase in the value of the items related to the importance of evidence. A qualitative analysis was conducted on the contents of the worksheets created by the children's self-initiated investigative study. The results showed that the children who expressed their own opinions during the investigation study were significantly more concerned about listening to the opinions of others who had different ideas than themselves than those who did not the investigation study.