The second Monday of October is Health-Sports Day. It is also called National Sports Day.
It was originally celebrated on October 10th to commemorate the opening ceremony of the 1964 Tokyo Olympics. The date of Health-Sports Day was changed to the second Monday of October by a new law called Happy Monday in 2000. Only the year of 2020 when the Tokyo Olympics is held, Health-Sports Day will be changed to July 24th.