Red 40 is allowed in Japan, as Red 40 also known as Allura Red AC is permitted and listed as an approved food color in Japan under Japan's Food Sanitation Law.
Although, while Red 40 is allowed in Japan, it's not commonly used in many products as a result of stricter regulations or even consumer preference for natural colors.
Although some sources also note that the restriction on Red 40 or avoidance is in favor of alternatives.
Japan's Ministry of Health, Labor and Welfare lists Red 40, (designated as "Food Red No. 40" or "Allura Red AC") as an allowed artificial color.
Japan mostly focuses on natural ingredients, as there's a growing trend and market demand in Japan for natural ingredients, which lead to many companies avoiding synthetic dyes, including Red 40 dyes.
While Red 40 is common in the United States, Japan has their own list, and other dyes like Yellow 6 Dyes, such as Sunset Yellow are actually banned in Japan.
Health conscious people also often look to avoid the additives like Red 40, and choose restaurants or products that use whole and fresh ingredients.
You might find Red 40 in Japan on some imported food products, but not often in Japan's own food products.