Contra has been around a long time, over 25 years now. But gambling has certainly been around much longer. Since then, companies like Konami thought it would be a good idea to combine the two for fans of both gaming and gambling.
Both Suikoden and Castlevania managed to land their own pachislot machine, so why not a Contra 3D machine? Recently they did just that, and launched a machine with all of the elements you've come to known and love from the series. This even includes music you should be familiar with. Even thought you might not be able to read Japanese, you can still check out an official page for the new gambling title here.
There are various pages there, some for showing you what the 3D graphics look like, along with characters, story mode, samples of music to listen to, and so fourth. Let me know what you think of it in the comment section below.