Abstract: [Problem to be Solved] To provide a gas humidity regulating method and a regulator that can regulate a temperature during humidity control and improve humidity-control efficiency. In an air humidity regulating method for gas subjected to treatment, a first medium 22 is caused to flow onto a heat exchanging pipe 17 of a gas-liquid contact part 18 in a dehumidifier 11; meanwhile, a second medium 24 is passed through the heat exchanging pipe 17. In this state, air is fed into a gas-liquid contact case 13 from an inlet port 14 and gas-liquid contact is made by the first medium 22 on the gas-liquid contact part 18 so as to absorb water content from the air into the first medium 22. The first medium 22 contains an ionic liquid having high absorbency. The temperature of the first medium 22 is regulated by the second medium 24. After that, treated air is discharged from an outlet port 15 of the gas-liquid contact case 13.