The popularity of prepared food, known as "sozai," is rocketing in Japan, with an increase in working women apparently helping to boost sales of the food.

"Taking out ready-made food and eating it at home has become more common," said Michio Goto, executive director at Kakiyasu Honten Co., which runs the popular Kakiyasu Dining chain.

The firm's sozai sales soared 105 percent in the year that ended Sept. 30.