A screw loosening prevention structure and a gas-pressure device are provided. The structure includes a first member that is formed with a container space filled with gas, and includes a first threaded portion, a second member that includes a second threaded portion, wherein the second member is threadedly coupled with the first member by threadedly engaging the second threaded portion with the first threaded portion, and receives a pressure from the gas in the container space of the first member, and a spring member provided between the first and second members in a deformed state in which the displacement of the spring member is greater than a relative displacement of the first and second members due to a loosening factor including the gas pressure that is received by this second member.