The Nikkei 225 index at the Tokyo Stock Exchange fell 11.95 points to 8,529.98 by the lunch break. The Topix index of all first-section issues sagged 0.23%, or 1.66 points, to 729.25.
After tracking a modest 0.14% gain for the Dow Jones Industrial Average overnight following positive retail sales data, the Nikkei fell back in mid-morning trade as concerns over the eurozone eroded risk appetite.
You can't buy stocks without reservations when it's unclear what is going to happen to the euro's levels," Kenichi Hirano, operating officer at Tachibana Securities, told Dow Jones Newswires.
Yoshihiro Okumura, general manager at Chibagin Asset Management, said: "Not much progress is seen in Italy though the situation eased somewhat with the new leader assuming his role."
Italian prime minister designate Mario Monti vowed to unveil a new government today to tackle the debt crisis, as bond rates hit dangerous highs.
He was scheduled to meet President Giorgio Napolitano at 1000 GMT before being officially sworn in.
Investors were cautiously watching the ability of newly appointed leaders in Italy and Greece to address their respective sovereign debt problems.
As persistent concerns sent the euro lower against the yen, major Japanese exporters with exposure to the continent came under selling pressure.
Among them, Sony dropped 1.92% to 1,327 yen and Honda was down 0.57% to 2,260 yen.