To provide an air plug for mutually connecting between two air tanks, especially an inexpensive bidirectional air plug having simple structure suitable for preventing noise and jumping motion of an air hose end part, and an air hose set and an air tank connection structure using the air plug.

The air plug is provided with an intermediate flow hole part 106 at the intermediate part 102 of a columnar body (cylindrical body) 100, and the diameter of the hole is made to be smaller diameter than those of the one end side flow hole part 105 and the other side flow hole part 107. The intermediate flow hole part 106 functions as a bottle neck hole part increasing the flow path resistance with respect to a compressed air flowing in the intermediate flow hole part 106 from the one end side flow hole part 105 or the compressed air flowing in the intermediate flow hole part 106 from the other side flow hole part 107.