PROBLEM TO BE SOLVED: To halt supply of a gas at an early point by quickly detecting leakage of the gas from the inside of a desired body cavity to the outside and the supply of the gas of the sufficient amount to the inside of the desired body cavity.SOLUTION: An air supply device 1 includes: air supply means 3, 4 for supplying a gas to the inside of a body cavity Y of a living body X； an intracavitary pressure measurement part 5 for measuring a pressure of the inside of the body cavity Y； a determination part 13 which determines whether the amount of a change per unit time of the pressure inside the body cavity Y that is measured by the intracavitary pressure measurement part 5 is within a prescribed range or not； and a control part 13 which halts the supply of air to the inside of the body cavity Y by the air supply means 3, 4 when the determination part 13 determines that the amount of a change of the pressure inside the body cavity Y is smaller than the prescribed range.
