PURPOSE: To prevent the decrease in the quantity of grain discharged at the end of the discharge port and also to prevent the uneven drying of grain resulting from a difference in the velocity of the grain flow by making the opening at both ends of a rotary valve larger than the opening of other parts.

CONSTITUTION: When the grain is fed from a grain tank 2 into a drying chamber 5 and dried by hot air therein, rotary valves 11 located on the bottom of the drying chamber 5 rotate so that the grain is discharged through the gaps between said valves and receiving plates 18. Since the opening 17 at both ends of the rotary valve is larger than the opening 17 in other parts, the flow of grain does not slow down at both ends of the rotary valve 11 and the grain flows in a constant quantity onto receiving throughs 9, carried by a screw conveyor 10 to a lift 3, thereby to be returned to the grain tank 2 so that the grain is circulated for drying.