PURPOSE: To make it possible to improve strength and reliability by radiating microwaves to the joint part of two ceramic items in a vacuum state and simultaneously applying compressive force thereto, then continuously monitoring the joint part.

CONSTITUTION: The microwaves are supplied by a magnetron 11 and are sent into the cavity 27 of a hermetic vessel 21 where samples S1, S2 are arranged. The cavity 27 is excited by a single mode microwave electric field form and the resonance frequency thereof is changed by adjusting the position of a rear surface wall 28. The electric power absorbed by the samples S1, S2 is measured as a difference between the electric power in an advancing direction focused into the cavity 27 and the electric power reflected and returned from the cavity 27. A compressor 309 exists on the outside of the vessel 21 and applies the compressive force on the sample S1, S2 in the joining process. A load cell 31 measures the force and transmits the data to a monitor and a recorder 38. The recorder 38 displays the data. The electric power absorbed during the joining, the elevated temp. and the applied pressure are monitored and are recorded as the function of time in the recorder 38.