Overview
Mount Jumai (Jumai-san) is a 1,726-meter peak straddling the border of Nanbu Town in Yamanashi Prefecture and Aoi Ward, Shizuoka City in Shizuoka Prefecture. Rather than a single summit, it is a twin-peaked mountain: the 1,726-meter Kami-Jumai (Upper Jumai) and the 1,732-meter Shimo-Jumai (Lower Jumai) rise side by side. On Geospatial Information Authority of Japan maps, Kami-Jumai is labeled as Mount Jumai. Quiet ridge walking between two prefectures, with grasslands and forest that change with the seasons, makes it a favorite for those who love unhurried mountains.
Highlights
- ●A twin-peaked profile of Upper and Lower Jumai
- ●A border ridgeline you can walk between Yamanashi and Shizuoka
- ●Quiet hiking through grasslands and forest
- ●Nature protected within the Okuoi Prefectural Natural Park
History
As one of the peaks along the Abe-higashi ridgeline dividing Yamanashi and Shizuoka, Mount Jumai long stood as a boundary between the living areas of the two prefectures. The Shizuoka side is designated part of the Okuoi Prefectural Natural Park, protecting its rich natural environment. Untouched by large-scale tourism development, it retains its distinctive twin-peak character while cartographers settled on Kami-Jumai as its representative summit.
Access
The mountain sits on the prefectural border near 35.25N, 138.38E, between Nanbu Town and Aoi Ward. Public transport to the trailheads is limited, so most hikers reach either the Shizuoka-side or Yamanashi-side trails by private car or taxi. Check current forest-road conditions, trailhead access, and parking with local authorities or official hiking information before you set out.
Best season
The mountain is most comfortable from early summer, when the grasslands turn vivid green, through autumn, when clear air sharpens the ridgeline views. Winter brings snow and ice that raise the difficulty and demand experience and proper gear. Weather and residual snow change quickly, so confirm the latest conditions through official sources before climbing.
Map
35.2539, 138.3778 · Wikidata
Suggested itinerary
- 1Check gear and weather at the trailhead before entering
- 2Climb through forest to the open grassland ridge
- 3Trace the twin peaks of Upper and Lower Jumai
- 4Enjoy the border views and descend safely by the same route
Did you know?
💡 The unusual name Jumai and the surprising fact that Lower Jumai (1,732m) is actually higher than Upper Jumai (1,726m) are quirks you notice only when you look closely at the map.
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