PURPOSE: To provide a vapor generation device which is capable of performing humidity adjustment correctly within a low humidity range.

CONSTITUTION: Air to be fed out of an air pump 9 is conducted into the interior of a water tank 6, and water 37 is pressed by pressure gradient which generates in both upper and lower end openings of an orifice pipe 18. Consequently, a very small amount of water is fed into an evaporation pipe 19, passing through a first water passage pipe 23 and a second water passage pipe 23, both having a fine inner diameter, and is evaporated. The vapor component generated by evaporation is mixed with dry nitrogen gas taken in from a gas intake hole 35 into vapor of desired humidity. Further, the density of this vapor is made uniform in a buffer chamber 8 of large dimensions, and is taken out to an outer area from an exhaust pipe 30. Humidity adjustment within a low humidity range is possible by feeding a very small amount of water to the evaporation pipe 19.