Actually that is a trick question. Nothing is big in Japan (unless you count my headache, borne of the endless string of English conversation students telling me they 'went to shopping.')
But all things are relative, and this sign stands as proof that karaoke is relatively big.
In case you are illiterate, the sign is for karaoke classes, taught by a woman by the name of Ito. Yes, there is, right down the road from me, someone who is ready (for some ridiculous amount of money I'm willing to bet) to teach me how to be better at karaoke. I can only assume she understands that the places I go to sing karaoke also offer all-you-can-drink deals. Not that a gallon of beer makes my singing any better but it sure helps my friends think so.
Of course, if karaoke were food I'd be eating at Bob's Big Boy. Ms. Ito, I think, is catering more to the Peter Lugar crowd. I sing karaoke in places with private soundproof rooms with people who know I have also had a gallon of beer. Ms. Ito's students sing karaoke in places with only one room, where everyone in the building can hear you and there is no vomit on the floor.
There are even karaoke competitions, with the regionals and national finals broadcast on television in the afternoons when the old folks are still awake. So while I may poo-poo the idea of karaoke classes as I ride my bike past Ms. Ito's place on my way to Bob's Big Boy, the reality is that Ms. Ito is into helping people better themselves in their own way.
Meanwhile the people in my classroom just keep going to shopping.