The world's third-largest economy grew by 1% during the April to June quarter - up from 0.4% between January and March, and well ahead of the 0.6% forecast by economists.
The figure was much higher than a median forecast of 2.5 percent growth among 21 economic research institutes polled by Jiji Press.
Exports fell 0.5% quarter-on-quarter for the first contraction in four quarters, while imports climbed 1.4%, the office said.
"If you ask me whether private consumption has fully recovered, I would say it still lacks strength in some areas, which will need to be followed with policy", Motegi told reporters.
Adding: "The pace of growth may moderate slightly, but we are still in recovery mode". Monday's figures are good news for the current prime minister Shinzo Abe - whose brief and underwhelming first term as Japan's premier came directly after Koizumi.
The GDP data suggest that domestic demand was becoming the main driving force for the Japanese economy in place of exports that had led economic growth since the second half of 2016. He pointed to a rise in air conditioner demand due to the heat wave and a recovery in new auto sales after the year-before slump caused by a fuel economy data manipulation scandal at Mitsubishi Motors Corp.
The Japanese economy has recorded its longest economic expansion in more than a decade after official data showed that it grew at 1% in the last quarter.
Private inventories didn't contribute to GDP.
Domestic demand should have the potential to pick up further in 2H17, thanks to the improvement in the labour market, Olympics-related construction demand, and modest rebound in credit growth.
Private consumption at restaurant and service industries was strong on the back of better employment and income situations.
The costs of the companies in the second quarter grew by 2.4%, while the expected increase of 1.2%. The last time the economy had a run of six consecutive quarters of growth was January-March 2005 through April-June 2006. Behind the uncertainty over the course of consumer spending is stagnant growth in wages even as labor demand is the tightest in more than 40 years.
The growth in personal consumption, which accounts for 60 percent of GDP, was supported by renewed demand for automobiles and household electric appliances, but is also believed to have been aided by favorable weather that pushed up spending by consumers. Meanwhile, imports were pulled up 1.4%.