To facilitate opening of a door by preventing the door from being intermeshed or locked, even when a room interior is brought into a high pressure state.
This door unlocking device 24 includes a latch 35 and a strike 40 provided in the doors 21 and 22. The latch 35 includes a latch bolt 36 capable of being engaged with/disengaged from the strike 40, and a coiled spring 37 which is provided on the base side of the latch bolt 36. High pressure in a room 5 is applied to a space of the strike 40 through a pressure leading path 41 from an opening 42 in the door 22. The latch bolt 36 engaged with the strike 40 recedes while compressing the coiled spring 37 under the high pressure introduced into the strike 40, so as to be disengaged from the strike 40. Thus, the doors 21 and 22 are brought into an unlocked state before deformation, even when the inside of the room 5 is filled with high-pressure gas.