Many visitors to Japan are concerned about the ingredients contained in the food and meals they purchase during their trip. Food labeling in Japan is regulated by the Food Labeling Act, which covers allergen labeling, expiration date labeling, and nutritional content labeling. The Consumer Affairs Agency has published a pamphlet describing food labeling in English, Chinese, and Korean for overseas visitors to Japan (see URL below). Please make use of this pamphlet when shopping for souvenirs, at supermarkets and convenience stores.
Restaurants and other dining establishments, as well as those that sell in-person or by volume, are not required to provide allergen information, but checking the Allergen Communication Sheet at the end of the pamphlet and presenting it at the establishment can help you avoid the onset of allergen-related symptoms.
(Source: Consumer Affairs Agency website)