To prevent generation of cracks, deterioration, burn or the like on a dried object in a microwave drying device, as the dried object gets over-dry by its abnormal temperature rise as the dried object is dried to a certain extent and latent heat depriving heat due to water evaporation gets smaller than microwave energy.

The device is so structured that a field intensity sensor 21 consisting of a receiving antenna 19 and a coaxial waveguide converter 20 is provided at a wall 17a of an applicator 17, monitoring signals of the field intensity sensor 21 are rectified and amplified, and the monitoring signals rectified and amplified are supplied to a display unit 23 such as a meter, so that, whenever display of the display unit 23 reaches a prescribed display value (a threshold value), an output power of a microwave oscillator 11 is controlled downward.