PURPOSE: To stabilize generation of dry air by limiting the amount of the outside air introduced to dehumidify and dry grains so that acting period of time between the grains and devices constituting a dehumidifying device is provided sufficiently.

CONSTITUTION: Outside air intake ports 9, 12 are provided respectively in spaces 5, 6 which are formed in front and in rear and a condenser 10 is provided in the space 5 and an evaporator 13 is provided in the space 6. Hot air having passed through the condenser 10 and dehumidified and cooled air having passed through the evaporator 13 are mixed together in a mixing space formed above the spaces 5, 6 and the mixture thus provided is mixed with the outside air in a proper manner to prepare dehumidifying and drying air.