PURPOSE: To exclude abnormal values due to the mixing of green rice or immatured rice and to control a drier accurately by measuring a load applied between electrodes, and judging the measured value as a normal water value when the measured value is between an upper and lower limit value which are predetermined.

CONSTITUTION: A sample to be measured is extracted from the drier and put in a lower electrode 6, and an upper electrode 4 is lowered by the driving force of a driving source to press the sample for loading. This load is detected by the load sensor 42 composed of a strain gauge 18 and its measured value is sent to a multiplexer 32 through an amplifier 30. The water value of the sample, on the other hand, is converted into a voltage which is sent to the multiplexer 32. Then, both signals are A/D-converted by an A/D converter 34 by a signal from a CPU 36 and sent to the CPU36, which obtains the upper and lower limit values of measured load values of normal grains from an ROM38 and judges whether the measured load is within said range or not to regards the measured water value as a normal value when the measured load value within the range, controlling the drier.