To avoid turbulence of a power distribution of a sound frequency to judge the propriety of internal pressure of a sealed container by separating the top wall part of a carton case from a hood part of the container before inspection of internal pressure by exciting forcibly a cover plate part of the sealed container.

A carton case restoring mechanism 12 is arranged on the upstream side from a can striking sound inspection mechanism 13 provided in a conveying passage (a belt conveyer) 11 of a carton case 2 storing a sealed container (canned goods) 1. An air cyliner 12a arranged on both sides of the belt conveyer 11 is extended to nip from both sides the carton case 2 conveyed by each air pressure-introducing part 12b, and compressed air is ejected from the part 12b to pressurize the inside of the carton case 2 from clearances of both sides of the carton case 2 to be inflated. A form of the caton case 2 deformed by a load form its upper side during storage is restored thereby, and the top wall part of the carton case 2 contacting with a cover plate part of the container 1 is separated from the cover plate part of the container 1.