What was the first Pokémon Stadium game released in Japan called?

The first Pokémon Stadium game released in Japan was called Pocket Monsters Stadium.

Nintendo released Pocket Monsters Stadium for the Nintendo 64 in 1998. It brought Pokémon battles into polygonal 3D and connected with the Game Boy Pokémon games through the Transfer Pak accessory.

Only 40 of the original 151 Pokémon were usable in this Japan-only release. A later and more expansive game was released internationally as Pokémon Stadium; in Japan, that follow-up was titled Pokémon Stadium 2. The regional naming difference causes frequent confusion.

The international Pokémon Stadium therefore was not the first Japanese Stadium title. Pocket Monsters Stadium came earlier, while the later game supplied the larger roster and broader features familiar to many players outside Japan.