I was presented a pot of the plant some years ago.
Then I planted it on the ground.
A lot of flowers bloomed till last year but the flower is few this year.
There are these blue flowers blooming in my yard now.
Though I didn't know the name for a very very long time, I found it's name O-O-tsu-ru-bo or Ryu-u-go-n-shi-su(Scilla peruviana) by looking it up in the article of 園芸ナビ.