At a Kaiten Sushi restaurant
Conveyor belt sushi is called "Kaiten Sushi" in Japan. It is known as "Sushi Train" in Austrian and you can enjoy it even in Paris and London.
In the restaurant there are rotating conveyor belts on which plates with sushi are placed move along every table and counter seat. Customers can pick as many sushi as they want. And they can order a sushi chef what they want directly or through a speaker phone.
Plates with different colours have different prices. But some restaurants have a fix price of 100 yen for all plates.
If you feel hesitant about eating raw sea food, you can find sushi topped with deep fried shrimp or grilled beef at a conveyor belt sushi restaurant, though they are never served at a genuine style sushi restaurant.