January 1, New Year's Day (Ganjitsu, or Gantan) The second Monday of January, Adults Day (Seijin no hi) February 11, National Foundation Day (Kenkokukinen no hi) March 20 or 21, Vernal Equinox Day (Shunbun no hi) April 29, Greenery Day (Midori no hi) May 3, Constitution Memorial Day (Kenpokinenbi) May 4, Greenery Day (Midori no hi) May 5, Children's Day (Kodomo no hi) The third Monday of July, Marine Day (Umi no hi) The third Monday of Septembe, Respect for the Aged Day (Keiro no hi) September 23 (or 22), Autumnal Equinox Day (Shubun no hi) The second Monday of October, Health-Sports Day (Taiiku no hi) November 3, Culture Day (Bunka no hi) November 23, Labor Thanksgiving Day (Kinrokansha no hi) December 23, Emperor's Birthday (Tenno tanjobi)
If you are planning a trip to Japan, I would advise you to avoid the following periods, because a lot of Japanese people make domestic trips, causing terrible traffic jams and difficulty in reserving plane/train tickets and hotels: New year holidays: from around December 27 through January 5. "Golden Week" (clustered national holidays and weekends): from around April 29 through May 5. Summer vacation coinciding with O-bon week: from around August 13 to 18.