To provide a method for detecting molten metal supplying quantity with which it can stably and accurately be judged that the molten metal supplied into a vessel reaches a prescribed quantity.

This method for detecting the molten metal supplying quantity, is the one for judging that the molten metal 10 supplied into a ladle 20 reaches the prescribed quantity with the output value of a laser sensor 19. A reference surface 22 is the upper surface of the reference part 21 formed by protruding in the ladle 20 and the laser sensor 19 is disposed at a fixed distance from the reference surface 22 to always measure the reference surface 22. Then, when the output value of the laser sensor 19 firstly exceeds an upper limit reference value or a lower limit reference value, it is judged that the molten metal 10 reaches the prescribed quantity. Further, the output values of the laser sensor 19 are averaged.