The men's 400 metre freestyle competition at the 2018 Pan Pacific Swimming Championships took place on August 11 at the Tokyo Tatsumi International Swimming Center.

[1] The defending champion was Park Tae-hwan of South Korea.

[2] Prior to this competition, the existing world and Pan Pacific records were as follows: All times are in minutes and seconds.

[3] Only two swimmers from each country may advance to the A or B final.

If a country not qualify any swimmer to the A final, that same country may qualify up to three swimmers to the B final.