Provided is an air supply tube including an inlet port that takes in air, an outlet port that is arranged opposite a portion of an elongated target structure in a longitudinal direction, to which air taken in from the inlet port is to be supplied, and has an elongated opening shape, a channel portion in which a channel space for allowing air to flow between the inlet port and the outlet port is formed, and plural suppressing portions that suppress the flow of air, wherein the plural suppressing portions include at least a most downstream suppressing portion, a first upstream suppressing portion that is provided in a part initially located on the upstream side in the air flow direction, and a gap regulating portion that forms an extended gap at the same interval.