TOKYO - Japan's population grew at its slowest rate since 1920 in the five years to 2010, data released on Friday showed, underscoring the challenges for policymakers struggling with the rising costs of an aging society.

Japan's population grew by 288,000 to 128.05 million, during the five years to October 2010, census data showed. That translates into a growth rate of 0.02 percent, the lowest on record and well below the 1945-1950 postwar peak of 15.3 percent.

"The 0.2 growth rate was slightly higher than expected, although it does not change the fact that the number of Japanese is likely to decrease," an internal affairs ministry official said.