Police on Wednesday raided the operator of Wonderland, an amusement park in Sakai, Fukui Prefecture, a day after a 6-year-old boy was injured on a roller coaster.

The boy suffered a fractured rib after being thrown out of the front seat of a two-seat roller coaster car and falling about 4 meters to the ground.

The police searched the offices of Sekiyama Kanko, based in Awara, Fukui Prefecture, the company which operates the amusement park, for alleged professional negligence resulting in injury.

Police also began investigating the site of the accident, inspecting the ride and questioning park officials about safety management.

A safety belt that allegedly was fastened over the boy when he got on the ride was found after the accident to be uncoupled, according to the police.