An insertion apparatus includes an endoscope, a first air feeding apparatus, a first air suction apparatus, a second air feeding apparatus, a second air suction apparatus, a pressure detector, an operation detector and a controller, and the controller performs first control on the second air feeding apparatus and the second air suction apparatus so that the amount of gas per predetermined time period fed from the second air feeding apparatus becomes equal to the amount of gas suctioned by the second air suction apparatus, and when the operation detector detects the operation and the pressure detector detects that the pressure in a subject changes from a first pressure to a second pressure, the controller maintains the first control to perform air feeding/air suction into/from the subject at the second pressure.