What is your transportation to Fukuoka, cruise, regular ferry (Camellia Line) or jet foil? Cruise docks one of the 3 wharf in the port. Camellia and jet foils arrives at the international passenger terminal in the port. Bus ride from the terminal to Hakata station is around 30 minutes. Taxi ride may be 15 - 20 minutes or less.
JR Bus departs from Hakata Bus Terminal, which is next to JR Hakata Station, for Hiroshima. The bus is reservation based. If it's not fully booked (probably in most cases except overnight bus), you can book it at the site.
ETflyer, thank you for your kind reply.
Do you have any website in English to book a ride bus?
If not I'll try to get a pass directly in at site. I´m trying book in a Japanese web site with the translate but it is not easy...
Hirofuku Liner Bus is a code share bus line by some companies, including JR Kyushu Bus. Except overnight ride, I don't think it's difficult to find a seat at Hakata Bus Terminal desk. Shinkansen train is highly competitive against expressway bus between 2 cities. If you're really keen to book, call directly 092-643-8541 or ask someone to book online for you in Busan. I don't think it's difficult for you to find someone who can read Japanese in Busan, either.