PURPOSE: To perform an accurate measurement of moisture by correcting the measured water content of grain particles with a water content meter provided on a dryer allowed for a difference from the actual water content while altering the correction as the dry level of the grain particles grows.

CONSTITUTION: A water content data voltage Er from a water content meter 2 provided on a dryer is converted into a digital voltage Es with an A/D converter 33 and inputted into a converting section 36 of a calculator 34 to be converted into a measured water content Ms in a digital value. Then, after a judgement on whether current measurement is initial one, the water content MSn at the (n)th measurement is calculated with an arithmetic section 37. The numeral of a water content MDn at the (n)th measurement is indicated on a display 35 as corrected according to a specified expression from the water content MSm thus calculated.