Okubo was named AFC Young Player of the Year in 2003 during his first stint with Cerezo, where he began his professional career in 2001.
 
In 2005 he moved to Spain to join Real Mallorca on a season-long loan and joined Vissel Kobe in 2007, while in 2009 he spent a six-month spell in Germany with Wolfsburg, where he was a member of the club’s Bundesliga-winning squad.

He returned to Vissel later that year before switching to Kawasaki Frontale in 2013, where he was to enjoy his most successful spell in the J-League.
 
Okubo finished on top of the scoring charts in 2013, 2014 and 2015 but was unable to help the club to the J-League title before departing to join FC Tokyo in 2017. A year later, however, he returned to Kawasaki for a short spell ahead of signing for Jubilo Iwata.
 
The striker then spent 2020 with Tokyo Verdy before returning to Cerezo at the start of this season to finish his career with his first club.

At international level, Okubo was a member of the Japan squad that represented the country at the Olympic Games in 2004 and was also part of Takeshi Okada’s squad at the 2020 FIFA World Cup in South Africa, when Japan reached the Round of 16. 
 
Okubo was also included in the 2014 FIFA World Cup squad selected by Alberto Zaccheroni for the Finals in Brazil.