To automatically monitor a residual amount of filament body even when a disk-shaped rotary unit is in rotation at a high speed.

This device is provided with a plurality of markers M corresponding to each shaft part 20 in a peripheral part of a disk-shaped rotary unit 12, and a marker detection means 110 for detecting one after another each marker M passing in the outward of this disk-shaped rotary unit 12, and a distance detection means 120 for detecting successively a separating distance from a peripheral surface in a side of the shaft part 20 corresponding to the detected marker M synchronously with detection of each marker M by the marker detection means 110 in the outward of the shaft part 20. By a residual amount monitoring part, each detection distance detected by the distance detection means 120 is discriminated to be present between an empty bobbin distance and a bobbin replacement distance to detect a bobbin replacement period.