Abstract: An air supply apparatus includes a plurality of movable carriages arranged along a circular carriage path; a movable circular duct arranged along the carriage path and connected to each of the carriages through a connection air duct; a water sealing device including a circular water seal chamber arranged along the carriage path and a water sealing plate having a lower end part thereof sunk in sealing water in the circular water seal chamber; a stationary circular duct arranged along the carriage path and fitted into the movable circular duct through the water sealing device to be freely movable, wherein the movable circular duct and the stationary circular duct form a circular air path; and an atmospheric zone that stops leakage of air in the carriage being provided in a predetermined position of the carriage path, wherein an upper space of the circular water seal chamber on a circular air path side communicates with the circular air path on a movable circular duct side, the circular air path on the movable c