PURPOSE: To stabilize the temperature of a treatment in treating a substrate to improve the reproducibility of the treatment of the substrate.

CONSTITUTION: A steam generating device is provided with treatment stagnating parts 3 and 4 for stagnating a substrate treatment, feed paths 45 and 50, steam generating parts 2 and 9, heaters 46 and 51 and a circulating path 52. The paths 45 and 50 feed the substrate treatment stagnated in the parts 3 and 4. The parts 2 and 9 evaporate the substrate treatment fed through the paths 45 and 50 while making the substrate treatment overflow them to generate the steam of the substrate treatment. The heaters 46 and 51 are respectively provided in the middles of the parts 45 and 50 and heat the treatment to pass through the paths 45 and 50. The path 52 circulates the substrate treatment made to overlow the paths 2 and 9 to the paths 45 and 50.