A soldering device for soldering leads of a lead component which is mounted on a board by jetting molten solder stored in a solder bath, wherein the soldering device includes a detection sensor capable of detecting a liquid level height of the molten solder inside the solder bath, and wherein the soldering device includes an estimation device for estimating the amount of molten solder inside the solder bath being characterized in that the estimation device includes a first estimation section for performing a first solder remaining amount measurement and for determining whether or not a detection height that is the liquid level height of molten solder which is detected by the detection sensor is greater than or equal to a first set height which is arbitrarily set, and, in a case where the detection height is greater than or equal to the first set height, estimating that molten solder of an amount capable of performing a soldering work for a predetermined number or more of boards by using the soldering device is stored in the solder bath, and a second estimation section for performing a second solder remaining amount measurement and for estimating the amount of molten solder that is stored in the solder bath by multiplying a difference between the detection height and a preset second set height by an area of the solder bath in a horizontal direction, and in that the soldering device further includes a controller including the first estimation section for performing the first solder remaining amount measurement and the second estimation section for performing the second solder remaining amount measurement after a first solder remaining amount measurement in a case where it is determined by the detection sensor that the detection height is not greater than or equal to the first set height and a replenishment of solder is not performed, and a solder replenishment device operated to replenish the solder bath according to the liquid level height of molten solder inside the solder bath detected by the detection sensor. wherein the soldering device includes a detection sensor capable of detecting a liquid level height of the molten solder inside the solder bath, and wherein the soldering device includes an estimation device for estimating the amount of molten solder inside the solder bath being characterized in that the estimation device includes a first estimation section for performing a first solder remaining amount measurement and for determining whether or not a detection height that is the liquid level height of molten solder which is detected by the detection sensor is greater than or equal to a first set height which is arbitrarily set, and, in a case where the detection height is greater than or equal to the first set height, estimating that molten solder of an amount capable of performing a soldering work for a predetermined number or more of boards by using the soldering device is stored in the solder bath, and a second estimation section for performing a second solder remaining amount measurement and for estimating the amount of molten solder that is stored in the solder bath by multiplying a difference between the detection height and a preset second set height by an area of the solder bath in a horizontal direction, and in that the soldering device further includes a controller including the first estimation section for performing the first solder remaining amount measurement and the second estimation section for performing the second solder remaining amount measurement after a first solder remaining amount measurement in a case where it is determined by the detection sensor that the detection height is not greater than or equal to the first set height and a replenishment of solder is not performed, and a solder replenishment device operated to replenish the solder bath according to the liquid level height of molten solder inside the solder bath detected by the detection sensor.