When entering Japan you must fill out a customs declaration about the items you are bringing into the country. These forms are usually handed out on the aircraft or ship before your departure, or they can be found in the customs hall.
Along with your passport you choose either the red channel if you have something to declare, or the green channel if you do not.
Once you are processed, you are then reunited with your on board luggage to be further processed by customs inspection officers, before being granted access to enter Japan.
Japan is extremely strict on what items can be brought into the country and exceptionally strong penalties exist for those doing the wrong thing, at the time of writing the following items were banned but please visit the Japanese Customs website for the latest up to date information.
Illegal drugs, including heroin, cannabis and other narcotics, firearms, ammunition’s and explosives, counterfeit money or credit cards, obscene, immoral material e.g. pornography in all forms including drawings, videos, carvings, DVDs or printed works and articles that infringe intellectual properties.
There are also restrictions on bringing certain organic items into the country including some animals and plants and strangely salt. If in doubt people should declare any item with the customs officers instead of risking severe fines and or long jail terms.
There are also some duty free restrictions with allowances of 3 x 760ml bottles of alcohol, 57g of perfume, 400 cigarettes and souvenirs and gifts up to Y200,000.
People bringing more than the equivalent of one million yen into the country in cash should also declare it. People bringing more than this amount into Japan can pay an additional charge at the customs office.
Japan Customs Website