In monitoring anomalies in a measurement process comprising a main measurement process Sa which performs a measurement by forward rotating a screw 3 having a back-flow prevention valve 2 installed on the tip and a post-measurement process which performs a post-measurement process Sb for closing said back-flow prevention valve 2 after this main measurement process Sa ends, after said post-measurement process Sb ends, an injection process Si wherein said screw 3 is put in a freely-rotatable state and moved forward is performed, the amount of rotation Rd of said screw 3 since the start of this injection process Si is detected, and if the detected amount of rotation Rd exceeds at least a preset amount Rs, an anomaly processing (S9) is performed.