TOKYO, May 23 (Reuters) - Superlong Japanese government bonds firmed on Tuesday after decent results at a liquidity-boosting auction, while the benchmark JGB was steady.
The 10-year cash JGB yield was flat at 0.045 percent, while 10-year JGB futures edged up 0.04 point to finish at 150.59.
The 40-year JGB yield fell 1.5 basis points to 1.015 percent, ahead of Thursday's sale of 40-year debt.
The 20-year JGB yield shed half a basis point to 0.560 percent, while the 30-year JGB yield fell one basis points to 0.795 percent.
But at the shorter end, the five-year yield added half a basis point to minus 0.120 percent, as investors awaited the details of the Bank of Japan's regular bond-purchasing operations for June, which will be announced next week.
The BOJ's massive asset purchase programme has reduced market liquidity. In an attempt to reduce volatility, the central bank has been adjusting its bond-buying. For both May and April, the central bank trimmed the amount of shorter-dated JGBs it bought compared with previous months. (Reporting by Tokyo markets team)