You can use Hiragino Sans GB for free only on devices where it is pre-installed (Mac, iPhone, iPad). You cannot legally:
The official partner for Hiragino fonts provides detailed specimens and licensing for international markets. 3. Free Legal Alternatives Hiragino Sans Gb Font Free Download
Hiragino is not a "free font" in the public domain. It is a proprietary font owned by Screen Holdings (Dainippon Screen Mfg. Co., Ltd.). You can use Hiragino Sans GB for free