To stabilize the quality of brazed parts and, at the same time, to prevent the deterioration of wettability of the brazed parts with a brazing material by monitoring such information as the atmosphere, temperature, optical information on brazing state, etc., on the inside and outside of, especially, inside of a liquid supplying and discharging box.

After conductor element wires 2 carrying a brazing material are inserted into a liquid supplying and discharging box 1 having one openable face out of four faces and a lid 3 is put on the box 1. Coolant supplying and discharging metallic parts 4 and a coil connecting piece 5 are welded to the box 1 in advance and a coolant supplying and discharging chamber 6 in the box 1 is made empty. The brazing state and temperature are monitored by means of a monitor 9 by inserting a fiberscope 7 and temperature sensor 8 into the box 1 from the metallic parts 4. The fiberscope 7 and sensor 8 are constituted so that they can be moved freely in the vertical direction, can be rotated, and can be cooled.