We have a binding treaty with the PRC to recognize the one china policy. We don't have official diplomatic relationship with Taiwan , but many segments of government to the Japanese business federation (Keidenren) work closely with Taipei counterparts. In regards to Taiwan -- we follow a policy of :
漸進的発達. This means something to the line of
Progress Collaboration.
One of the LDP members, Councillor Kishi Nobuo , who happens to be the younger brother of Prime Minister Abe, has authored a legislative bill to establish a Japan-Taiwan Relations Act. This would provide judicial, economic and to some extent political and military support to Taiwan.
To Counter Beijing, Japan Moves Closer to Taiwan | The Diplomat
http://openasia.asia/can-they-be-best-friends-normalization-of-japan-taiwan-relations-1255