http://book.asahi.com/reviews/reviewer/2017052800009.html

http://kanz.jp/hanrei/data/html/201704/086857_hanrei.html

https://jp.reuters.com/article/japan-labor-shortage-idJPKBN19E0JA

http://gendai.ismedia.jp/articles/-/52035

http://blog.goo.ne.jp/yuasah1970/e/057d88c6c94f3d6db81b6ff35d6f1b0d