Unused foreign bills and coins brought home by Japanese travelers as well as leftover yen nestling in the pockets of departing foreign visitors are creating business opportunities at the nation’s airports.

A Tokyo-based venture began setting up machines last year allowing travelers to exchange leftover currency for electronic money or gift vouchers.

“There’s no way I can use” foreign currency at home, said a 21-year-old university student returning from the United States in January, who converted several dollars into gift vouchers at a Pocket Change machine. He was just one of many travelers at Haneda airport changing money at the machines, which can be operated in four languages — Japanese, English, Chinese and Korean.

Pocket Change Inc.’s machines accept the U.S. dollar, euro, Chinese yuan, South Korean won or Japanese yen, and both bills and coins, offering a range of e-money and vouchers for those living in Japan and abroad. For residents of Japan, e-money options include Rakuten Inc.’s Edy and Aeon Co.’s Waon.

Users can also choose vouchers from Amazon.com. Inc. or other outlets, or make a charitable donation with their unspent holiday cash.

Installing its first machine at Haneda in February 2017, Pocket Change now has least 15 units in Japan. The other airports that are now home to its machines are New Chitose, Chubu Centrair International, Kansai International and Fukuoka airports, and the firm is also operating units at hotels and department stores.