Surface 27 of molten metal within a mold is constantly monitored by camera 25. Camera 25 records the surface from an obliquely upward position of the mold in an area that does not affect the casting process. Various analyzing frames such as analysis band 35, molten metal pattern 37, and injection monitoring part 43, are set with respect to the information recorded by the camera 25. The analysis band 35 includes the surface (molten metal part 31c), and is set to a predetermined width so that the direction of surface change is in the longitudinal direction. The width of the analysis band 35 is set as wide as possible in a range that does not block the discharge part (molten metal part 31a). Inside the analysis band 35, the rate of change of the binary data is calculated by the analyzing part.