"As of March 27th
Foreigners who have been in the following countries in the prior 14 days: Iceland, Ireland, [EDIT]Andorra, Italy, Iran, Estonia, Austria, Netherlands, San Marino, Switzerland, Sweden, Spain, Slovenia, Denmark, Germany, Norway, Vatican, France, Belgium, Portugal, Malta, Monaco, Lichtenstein, Luxembourg.
Additionally, Hubei and Zhejiang provinces in China, as well as holders of passports from these regions.
Also a bunch of regions in South Korea (大邱広域市,慶尚北道の清道郡,慶 山市,安東市,永 川市,漆谷 テ グ ケイシヨウホクドウ チヨ ンド キヨンサン アン ドン ヨンチヤン チ ルゴク 郡,義城郡,星州郡,軍威郡 ウィソン ソンジユ グンウィ)
And lastly, passengers on the Westerdam cruise ship.
Source: Japan Ministry of Justice -- http://www.moj.go.jp/content/001316538.pdf