PURPOSE: To lessen the unevenness of grain drying in a square storing bin in a drying device provided with stirring screws in the storing bin to accelerate the stirring of the grain.

CONSTITUTION: Two stirring screws are provided vertically in each storing bin and such screws are so constructed as to stir grains while rotatably moving back and forth or from side to side. The screw stirring method comprises, in combination, a first pattern P1 wherein, after the screw is rotatably moved from one corner part (a) of the four corners of the bin as a starting point and approximately along a predetermined inner wall surface (b), it is further moved along the entire surface and to the other corner part (c), a second pattern P2 wherein, after the screw is rotatably moved from the corner part (c) as a starting point and approximately along an inner wall surface (d) different from the inner wall surface (b), it is further moved along the entire surface and to another corner part (e) and third and fourth patterns P3 and P4 wherein the screw moves in the same manner approximately along the remaining inner wall surface (h), whereby the grains are stirred to reduce the height of accumulated grains near the inner wall surfaces so as to accelerate ventilation.