PROBLEM TO BE SOLVED: To provide an air supply apparatus capable of determining whether or not air can be properly supplied to the inside of a lumen in a state that a treatment instrument is inserted into a treatment instrument insertion channel.SOLUTION: An air supply apparatus 21 includes an air supply pipe line 21C provided between a connector 21A for an air supply tube and a connector 21B for a cylinder, a control part 58, and a message display part 47. After air is supplied to an air supply tube 24 through the air supply pipe line 21C in a state that a treatment instrument 31 is inserted into a treatment instrument insertion channel 19, the control part 58 measures the time from when the air supply is stopped until a pressure P inside the air supply pipe line 21C reaches a predetermined value TH2. Based on the time measured, the message display part 47 outputs, by a message, the information indicating whether or not an endoscope 11 can be used in combination with the treatment instrument 31, and, if the endoscope 11 cannot be used in combination with the treatment instrument 31, the information on an endoscope that can be used.
