In English:
1. Search PAJ (search for terms in English summaries of
Japanese patents, or input the number of a Japanese Patent Publication)
https://www19.j-platpat.inpit.go.jp/PA1/cgi-bin/PA1INIT?1431436967645

2.Search Patent and Utility Model Gazette (enter the number of the 
patent or utility model for a summary in English, or find English machine
translations of patents issued after 1996)
https://www4.j-platpat.inpit.go.jp/eng/tokujitsu/tkbs_en/TKBS_EN_GM101_Top.action

3. Search for other functions from the English 
Home Page of the Japan Patent Office
https://www.j-platpat.inpit.go.jp/web/all/top/BTmTopEnglishPage

(Note: When the JPO website server is busy, you can access English summaries
and original text of Japanese (Kokai) patent applications from the search
pages of the European Patent Office and German Patent Office websites.)

In Japanese:
4. Search Japanese Patent Office Database in Japanese 
(特許・実用新案公報ＤB)
https://www.j-platpat.inpit.go.jp/web/tokujitsu/tkbs/TKBS_GM101_Top.action

5. Search Patent and Utility Model Gazette in Japanese
(search the front page of Japanese patent applications
with technical terms in Japanese)
https://www.j-platpat.inpit.go.jp/web/all/top/BTmTopPage

6. Search for other functions from the Japanese 
Home Page of the Japan Patent Office (特許庁ホームページ)
https://www.jpo.go.jp/indexj.htm