Forfeited jewelry, watches and other goods worth an estimated 400 million yen were stolen early Sunday from a public hall in Gifu, police said.
The hall was providing the venue for a four-day sales fair that got under way Friday, the Gifu Prefectural Police said.
The police said they found the entrance to the hall broken open with a tool similar to a crowbar.
The forfeited goods, offered for sale by pawnbrokers in Tokyo, Osaka and Kyoto, were in unlocked showcases.
The hall's security guard, who made his rounds around 1:30 a.m., called police after finding the door open.
The police quoted the guard as saying he had found nothing unusual when he made his earlier rounds at around 11:30 p.m. Saturday inspecting the building from the outside.