Hiroshima Station Details

At Hiroshima Station, which direction to exit to transit to Sanyo Line to Mukainada Station?

You have to exit the Shinkansen gates and head to local JR lines. The Sanyo main line is usually on tracks 3 and 4. The local lines run parallel to the Shinkansen lines and are located south of the Shinkansen lines. There is a corridor heading to the South exit of the station which you must take to get to the local JR lines.

Here is the map to the station (in Japanese, but you can figure it out): http://www.jr-odekake.net/eki/premises.php?id=0800613

Please see the station map which John B digs Japan put a link to.
From the Shinkansen zone, you can move to the non-Shinkansen zone through a transfer gate.
From the Shinkansen platform on the 3rd floor you can go downstairs using a staircase, an escalator or an elevator. Then find an information center, which is shown on the station map by a question mark in a circle. The gate nearby is the transfer gate between the two zones, which is shown by red short lines.
Make sure that the sign above your gate does NOT say you are exiting the station.

Tracks 3 and 4 are shared by trains running on thee lines (San'yo, Kure and Kabe) in different directions. You had better ask a station attendant which train you should take.
Local trains running for Kaitaichi, including those running to Kure Line, stop at Mukainada. Rapid trains skip it.

I assume you are going to the Mazda Museum & Factory tour?

Last time when I e-mailed them to book they suggested which train will be best so that you arrive on time as you cannot be late for the tour (it leaves on a bus from the main building so you can't "catch up"). I just checked the latest hyperdia timetable so I'd suggest either the train leaving Hiroshima at 9:15 which arrives at 9:21 at Mukainada, or the 9:31 which arrives at 9:37. This of course might depend on which exact date you are visiting so check hyperdia for details
http://www.hyperdia.com/

Enjoy your Mazda tour!

Appreciate all for the valuable information. Yes i am heading to mazda museum. Think like most of us The main issue is always the japanese wordings. Thank you.