Soldering can be performed in a state where the temperature in an object zone is stable, regardless of the heat capacity of a soldering object. A soldering device includes: a position calculation unit which calculates the position of a heated object according to operational information of a conveyer which sequentially transfers the heated object into a plurality of zones for heat processing communicated with each other; a heat capacity calculation unit which calculates the heat capacity of the heated object; and a temperature management unit which controls the temperature in an object zone into which the heated object is carried, upon receiving positional information from the position calculation unit. The temperature management unit feedforward-controls the temperature in the object zone by adjusting the heat capacity of the object zone according to the heat capacity calculated by the heat capacity calculation unit.