The 26-year-old midfield player, who will become the first Japanese player to appear in France's top division having achieved the same distinction in Portugal, has agreed a one-year contract. Montpellier finished 16th in Ligue 1 last season.
Hiroyama began his career with J-League side JEF United before joining Paraguayan club Cerro Porteño and then Braga. His attacking contributions from midfield won him a first international cap, but he missed the 2002 FIFA World Cup finals through injury.
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