Three men pleaded guilty Friday to professional negligence resulting in death as their trial opened in the death of a 6-year-old boy whose head was crushed in an automatic revolving door at Tokyo's Roppongi Hills.

Ryo Mizokawa from Suita, Osaka Prefecture, got his head stuck between a revolving door and the frame as he rushed ahead of his mother into an entrance on the second-floor of the Mori Tower building at the commercial complex in March 2004.

Yuzo Tada, 62, a former managing director of Mori Building Co.; Yukihiro Koyama, 48, a former Mori Building official in charge of Roppongi Hills operations; and Hisanobu Kubo, 62, a former director of Sanwa Tajima Corp., the manufacturer and distributor of the door, all told the Tokyo District Court they were criminally responsible.

Prosecutors told the court that the two Mori Building officials failed to implement safety measures proposed by Sanwa Tajima because they were concerned the steps would detract from the appearance of the building's entrance.

The prosecutors also read a statement from Mori Building President Minoru Mori, included in an investigation report, in which he said the firm should have implemented all the safety measures instead of placing priority on the appearance of the popular complex.

They also said there had been 49 accidents at revolving doors of structures operated by Mori Building before the death of the boy.

According to the indictment, there had been a number of accidents in Roppongi Hills revolving doors since the complex opened in March 2003, including four months before the fatal accident when a 6-year-old girl was seriously injured.