PURPOSE: To provide a high-temperature corrosion-monitoring apparatus which can measure the presence/absence of piling and melting point of a compound of a low melting point in burnt ashes piled on the surface of a boiler equipment during the operation of the boiler.

CONSTITUTION: A plurality of electrodes 2 spaced at a predetermined distance, cooling means 7 and 8 for the electrodes 2, and a detecting means for detecting the presence/absence of a compound of a low melting point piled between the electrodes and/or a melting point of the piled compound by measuring a current value between the electrodes when a direct current voltage is impressed between the electrodes are set at the surface or in the vicinity of member of the boiler equipment where high temperature corrosion is easily caused by the compound of a low melting point in burnt ashes.