Condemned serial murderer Tsutomu Miyazaki has authored a book that compiles his letters to a publisher, branding the Supreme Court "an idiot" for sentencing him to death for killing four girls, the publisher said.

In the book "Yumeno Naka, Imamo" ("Still In A Dream"), Miyazaki, 43, calls himself "a popular man" because of the major news coverage after the top court last month upheld his death sentence.

On the murders he committed in 1988 and 1989, Miyazaki says he feels good as he "did good things." He has yet to apologize to the victimized.