To save spacing by performing drying and storing in the same place to utilize and make use of organic materials of a high water content as biomass resources.

The biomass resources may be efficiently obtained in a few sites as drying of the organic materials 21, 22, ... and storing of the dried organic materials 21, 22, ... are performed in the same place by alternately laminating the organic materials 21, 22, ... and impervious sheets 31, 32, ... by laying impervious sheet 31 on the organic material 21 after laying and drying the organic material 21 of proper layer thickness and then repeating a step where the undry organic material 22 of proper layer thickness is laid on the impervious sheet 31.