PURPOSE: To extremely quantitatively set soldering conditions by detecting the fact that conductor portions of a supply solder and a ceramic substrate form an electrically closed circuit.

CONSTITUTION: When a solder material 3 is supplied to a portion (a) of a ceramic substrate 1, i.e., a portion surrounded by a conductor 2 to be melted, the material 3 is supplied to only the interior of the portion (a) if mounting conditions are improper, and an electrically closed circuit of a power source 6, a detector 7, the material 3, the conductor portion 2, a mounting unit 5 and the power source 6 is opened so that the detector 7 does not operated. However, when the mounting material is extended to fill the portion (a) to arrive at the conductor portion 2, the circuit is closed so that the detector 7 operates. When the supply of the solder material is stopped, a suitable amount of solder material is supplied.