Style in the movie Big

18-year-old Kang Gyung-Joon's (Shin Won-Ho) spirit suddenly finds itself in the body of 30-year-old Seo Yoon Jae (Gong Yoo) . Seo-Yon-Jae is a successful doctor and engaged to high school teacher Gil Da-Ran (Lee Min-Jung). Gil Da-Ran just so happens to be the teacher of 18-year old Kang Gyung-Joon. More problems ensue when 30-year-old Seo Yoon Jae falls in love with another woman (Bae Suzy).

Source : http://asianwiki.com/Big_(Korean_Drama)