In 2002 season, he scored 18 goals which was the second top scorer and Cerezo reached the second place and was returned to J1 in a year.

Although the club results were bad, Mallorca finished at 17th place and remained La Liga in 2004–05 season.

On 3 January 2009, Vissel Kobe announced Okubo's transfer to VfL Wolfsburg of the Bundesliga.

At the end of 2016 season and before J.League Championship, Okubo announced he would leave Kawasaki Frontale to sign for FC Tokyo in 2017.

He made his international debut on 31 May 2003 in a friendly against South Korea at Tokyo National Stadium when he was sent on to the pitch to replace Takayuki Suzuki.

In August 2007, Okubo was selected Japan for the first time in 2 years by manager Ivica Osim.

[10] Okubo scored his first international goal on 17 October 2007 in a friendly against Egypt at Osaka Nagai Stadium.

Okubo's selection for the 2014 World Cup in Brazil was the big surprise of coach Alberto Zaccheroni's squad announcement.