A US Marine helicopter takes off from Futenma air base in Okinawa.
SDP chief Mizuho Fukushima informed reporters about the decision on Sunday after meeting with party executives. The move follows a dispute within the cabinet over the US airbase in Okinawa.
Fukushima, who calls for the immediate relocation of the base, has slammed Prime Minister Yukio Hatoyama’s decision to keep the US compound on the island — despite his campaign promises to relocate the base.
The airbase has been under US command since after World War II. More than half of some 47,000 US troops in Japan are stationed in Okinawa.
The issue has become the biggest challenge to Hatoyama’s government since it came to power. The premier’s failure to appease the islanders has dramatically reduced his public approval rating.
Okinawans want the airbase off their island. They say the US military presence is a source of noise and crime.
SDP’s defection is a tough blow to Hatoyama’s party. The Democrats need the help of other parties to win a majority in the Upper House elections.