TOKYO — Since Japan began counting its newborns more than a century ago, more than a million infants have been added to its population each year.

No longer, in the latest discomforting milestone for a country facing a steep population decline. Last year, the number of births in Japan dropped below one million for the first time, the Ministry of Health, Labor and Welfare said on Friday.

The shrinking of the country’s population — deaths have outpaced births for several years — is already affecting the economy in areas including the job and housing markets, consumer spending and long-term investment plans at businesses.

For now, the Japanese economy is growing despite a dwindling number of workers and consumers. Output rose for a fifth straight quarter at the start of this year, and the stock market reached its highest level in a year and a half on Friday, with the Nikkei-225 index exceeding the symbolic 20,000 mark. Growing global demand for Japanese products is one reason.