To uniformly heat even thick refractory and to improve operation efficiency.

Microwave is emitted to a refractory placed on microwave drying equipment (S3), the leaked microwave leaked from the microwave drying equipment is detected (S4) at a position separating from the microwave drying equipment by a prescribed distance L, an intensity of electric field of the detected leaked microwave is measured (S5), and an output of the microwave emitting to the refractory is controlled (S7, S9) when the intensity of electric field of the measured leaked microwave becomes more than a management value (first management value or second management value).