Rice prices set a record high for a fourth consecutive month amid rising production costs. Wholesale prices paid to farming cooperatives rose 60 percent in December compared with a year earlier.

The agriculture ministry says the average was 24,665 yen per 60 kilograms. That's 158 dollars and is the most since the ministry began surveying such data in 2006.

Ministry officials said competition among buyers to secure supplies following shortages last year also drove prices higher.

Businesses including restaurants and food makers have also begun passing the increases along to customers.

The country's largest convenience store chain 7-Eleven will raise prices for 40 percent of its rice products starting late this month. Popular items such as onigiri rice balls and boxed lunches are among those expected to see increases.