The baby business is BOOMIN' for Antonio Brown -- his girlfriend just gave birth to their brand new son! 

The Pittsburgh Steelers wide receiver was able to get away from football Tuesday for the birth of Apollo Brown

(It helps that today was a scheduled off day for Steelers players!) 

Both baby and daddy looked great (Antonio had a big smile on his face) -- hopefully mom, Chelsie Kyriss, is doing well too. 

It's AB's 5th kid -- 3 with Chelsie and 2 from a previous relationship. 

Congrats!