PURPOSE: To enable automatic detection of moisture value of chaff reaching a set finished moisture value during the circulating drying, by providing a moisture detection box or the like in which supply chutes and discharge chutes are connected at proper points during the circulation process of a chaff dryer.

CONSTITUTION: A moisture detecting box 3 in which supply chutes 4 and discharge chutes 5 are connected at proper points separately during the circulation process of a chaff dryer is provided. The detection box 3 is provided inside with a hulling roll 7, a hulled rice flow plate 8, a selective blower 10 with a air jet port 11 on the end side of a chaff flow grain plate 9 and a moisture detection roll 12 in the order. An automatic changeover shutter 14 is pivoted crawlingly between the end side of the supply chute 4 and the roll 7. Chaff supplied into the detection box 3 is fed onto a flow grain plate 5 and after separated by the blower 10, it is fed to rolls 12 and 12 to perform a moisture value detection work. At this point, as the moisture value approaches a preset value, the chaff is fed to rolls 7 and 7 being switched with the shutter 14 to perform hulling. In this manner, all chaffs can be dried accurately to meet a preset finished moisture value.