Convenience store sales nationwide fell 0.3 percent in 2017 on a same-store basis to ¥9.47 trillion, due partly to intensified competition with other retailers, according to an industry body.

The overall sales of eight major store operators declined despite a 1.5 percent increase in average spending per customer. Total sales, including those at outlets newly opened during the year, grew 1.8 percent to ¥10.7 trillion, the Japan Franchise Association said Monday.

Meanwhile, the association traced the rise in average spending per customer to higher sales of foods cooked within the stores on the back of the aging population and an increase in single-person and double-income households.

In December, the same-store sales of eight major convenience store operators totaled ¥820.5 billion, down 0.3 percent from a year earlier.

Customer visits fell 1.6 percent to 1.28 billion, while average spending per customer rose 1.4 percent, the association said.