Having a few drinks is perfectly acceptable; the emphasis on Shinkansen trains is quiet stress-free travel (even loud mobile phone conversations aren't allowed). BUT, do not become intoxicated (i.e. drunk) on board (or any other public space in Japan) to the point of being loud/obnoxious/rude/physically violent etc.

Yes, you are fully permitted to drink alcohol on the Shinkansen (bullet train) in Japan, and it is a widely accepted part of the travel culture. Unlike many Western rail systems that have restricted or banned alcohol, Japanese trains have no such rules. You can bring your own beer, sake, or "Strong Zero" purchased at a station Ekiben kiosk or convenience store (like 7-Eleven or Lawson) and consume it at your seat. In 2026, while many "cart services" (trolleys) have been phased out on certain routes in favor of station-side vending and pre-ordering, you can still find alcoholic beverages for sale at almost every major Shinkansen platform. The only "unspoken rule" is one of etiquette: passengers are expected to drink quietly and responsibly. Rowdy behavior or loud talking is highly frowned upon in the "silent" environment of a Shinkansen carriage. You should also be careful with strong-smelling foods or spills, as the trains are kept meticulously clean. As long as you are respectful of your neighbors, enjoying a cold "asahi" while watching the Japanese countryside fly by at 300 km/h is a quintessential and perfectly legal Japanese travel experience.