From the article:

Also known as Vulcan Venture, Gradius II launched in 1988 and was ported to the Famicom, PC Engine CD and Sharp X68000 – all of these ports were exclusive to Japan. The coin-op was later released on Saturn and PS1 in the Gradius Deluxe Pack and PSP as part of Gradius Collection. The game has also been released on Switch and PS4 as part of Hamster’s Arcade Archives collection.

This is not to be confused with the MSX Gradius 2, which is a completely different game.