To provide the method and apparatus, which can monitor the characteristics of yarn, which is running at a high speed, incessantly with highly accurate resolution.

In this method and apparatus, a body 1, i.e., yarn, roving, sliver and the like, is measured with a simple, adequate-cost sensor 5. Furthermore, a complicated sensor 8, which is accurate but slow in motion, is installed. When a specific phenomenon is indicated by the simple sensor, the sensor 8 is triggered with a sensor 5. Such a specific phenomenon is stored in the complicated sensor and accurately analyzed later for the sufficient time. All time interval between the occurrences of the two specific phenomena can be used for this analysis.