Vegalta Sendai's 1-0 home defeat by relegation-threatened Albirex Niigata gifted Hiroshima the trophy with one match to spare in the 2012 season.
Hiroshima have 61 points from 33 games, four points more than Sendai.
A goal blitz from Yojiro Takahagi, Toshihiro Aoyama and Hisato Sato put the home side 3-0 up at halftime before a fourth from Hironori Ishikawa.
Cerezo grabbed a consolation through a Takuma Edamura header.
Hiroshima's first major piece of silverware secured them a place in the seven-team Club World Cup from Dec. 6-16 alongside England's Chelsea and Corinthians of Brazil.
"We've come through some hard years to get here," captain Sato told reporters.
"Maybe we haven't always been the most attractive team to watch but this success is a result of the terrific support from out fans."
- Sports & Recreation
- Albirex Niigata
- Vegalta Sendai