To provide a method for easily and accurately estimating the temp. lowering rate of molten steel according to the repairing conditions and the eroding conditions of a steelmaking furnace and a ladle.

The estimating value of the temp. lowering rate of the molten metal at the temp. of carrying the molten metal tapped from the steelmaking furnace to the following process, is calculated (S1-S3). The temp. lowering rate of the molten metal by carrying with this carrying vessel is actually measured and the estimated value is corrected based on the difference between the actual measured value and the estimated value of the temp. lowering rate (S4-S6). Changing quantities of the differences just before repairings of the steelmaking furnace and the carrying vessel and the differences just after repairings, are stored respectively, and at the time of the next repairings of the steelmaking furnace and the carrying vessel, the estimated values of the temp. lowering rate are corrected based on the stored changing rate (S7-S9). By this method, the temp. lowering rate in the steelmaking process is calculated (S10). A target temp. of the molten metal tapped from the steelmaking furnace is calculated so that the molten metal temp. in the following process becomes a prescribed temp.