To provide an abnormality detection method and an abnormality detection device that can detect abnormality in a weft length-measuring and storing device without being affected by a noise.

In the abnormality detection method and the abnormality detection device, when a motor 5 for a pre-winding operation comes into a regular rotation state, a measuring means 22 measures the measured number of detection signals from an output of a rotation detection sensor 20. When a measurement time corresponds to a target detection time, a comparing and determining means 23 compares a measured number of detection signals measured by the measuring means 22 with a target number of detection signals. When the measured number of detection signals corresponds to the target number of detection signals, the comparing and determining means 23 determines that a weft length-measuring and storing device 1 is in normal condition, and stops the pre-winding operation. When the measured number of detection signals does not correspond to the target number of detection signals, the comparing and determining means 23 determines that a weft length-measuring and storing device 1 is in abnormal condition, stops the pre-winding operation and performs interlock operation so that the loom cannot activate. Also, an abnormal signal is output on a display device 25 to indicate an abnormality in a weft length-measuring and storing device 1. Thus, an abnormality in a weft length-measuring and storing device 1 can be accurately detected without being affected by a noise and the like.