The importance of critical thinking in science education is widely recognized. However, little research has been conducted on the teaching of critical thinking by teachers. If actual teaching conditions of teachers in the classroom are clarified, effective teaching methods for developing critical thinking in students could be developed. This study administered a questionnaire survey to ascertain how science teachers teach critical thinking in Japanese primary schools. The study population consisted of 291 Japanese primary school teachers with teaching careers spanning 1-38 years. The survey revealed the following: (1) teachers taught students the importance of conducting experiments by themselves to obtain results. However, teachers did not sufficiently teach students the need to conduct multiple experiments before reaching a conclusion, improve data reliability before making decisions, or examine their conclusions carefully given incomplete data; (2) compared to teachers with shorter teaching careers, teachers with longer careers taught critical thinking more effectively, particularly in terms of emphasizing positivity and maintaining a healthy skepticism; and (3) teachers who taught emphasized positivity and encouraged multifaceted thinking were more likely to teach about emphasized evidence. The corresponding causal relationship analysis suggests that teaching that emphasizes positivity and encourages multifaceted thinking is key to promoting evidence-oriented instruction.