Japan's monetary base rose 20.3 percent in June from a year earlier to 102.76 trillion yen, up for the 29th straight month, the Bank of Japan said Wednesday.
The monetary base -- cash in circulation plus money in current accounts held by financial institutions and Japan Post at the central bank -- rose 16.7 percent in May.
Japan Post started its transactions with the BOJ in April, coinciding with its launch as a public postal corporation.
The monetary base increase in June marked the 22nd straight month of double-digit rises.
The balance of current accounts at the BOJ increased 91.8 percent in the reporting month to 28.85 trillion yen. The balance rose 72.6 percent in the previous month.
The monetary base has been growing rapidly since March 2001, when the BOJ adopted a policy of quantitative monetary easing by injecting funds into the banking system to stem deflation.