Already more than 164,000 fans have turned out for the three games to date and Welsh coach Ruddock is hoping for another big gate to round off the series.
"It would be absolutely fantastic if the Millennium Stadium were forced to open the lower tier for the game on Friday night. I think they have to get advance sales of more than 40,000 to do that, so let's hope the sales keep going well and we get close to another full house," said Ruddock. "There is little doubt that the backing of the Welsh fans on Saturday had a huge impact on the Welsh players. The atmosphere was white hot - the best ever at the Millennium Stadium.
"The way the fans joined in with the response to the New Zealand Haka showed Gareth Thomas and his players that they weren't alone out there against the All Blacks.
"It made me feel proud to be Welsh when I heard Bread and Heaven ringing around the stadium before kick-off. It built our boys up and put the All Blacks on the back foot.
"It would be great for the players who play on Friday night to experience something similar. We've made a few strides forward in this series, but it is vital we win this last game.
"That's why I want to see as many people as possible cheering us on against Japan.
"We had two very near misses against two of the top teams in the world and a victory over Romania. We have to use the game against Japan as the springboard to our next Test assignment - against the world champions England in the Six Nations.
"Tickets for the game against England won't be easy to come by, so if mums and dads want to bring their children to see this Welsh team in action then Friday night against Japan is the perfect opportunity."
Tickets for the final game in the Lloyds TSB Autumn Series are £8 for adults and £4 for children if bought before the day of the game. On the day they rise to £10 and £5.
Tickets are available from the Millennium Stadium Ticket Office, 98, St Mary Street, Cardiff, via the WRU website, www.wru.co.uk or from Ticketmaster 08705 582 582.