Earth grossed $5.12m (Y550m) over the three-day holiday weekend period (Jan 12-14) on 275 screens. It's per screen average over the standard two-day period ($3.3m) was a strong $12,000.
The figures represent the widest and best opening ever for a documentary in the territory as well as the most successful opening for distributor Gaga Communications, beating previous record holder The Phantom Of The Opera (final gross $39.1m), released in 2005.
With eco-minded consumer trends sharply increasing in Japan, Gaga marketed the documentary more aggressively than is usual for the genre, with merchandise and exhibition tie-ups and special campaigns for discount tickets.
While Patrick Stewart provided narration in the original, Gaga enlisted star Ken Watanabe to record a Japanese track.
Directed by Alastair Fothergill and Mark Linfield, Earth follows the migration patterns of different animals in over 200 locations around the world, spanning the North to the South Pole. The German-UK co-production is billed as the most expensive documentary ever made and was shot using special cameras and lenses.
The other major opening was Toho's Season Of Snow. Produced by Fuji TV, the extreme winter sports action movie, directed by Umizaru helmer Eiichiro Hazumi, opened on 266 screens but only managed about half of Earth's box office take, coming in third behind I Am Legend.