To provide a system for detecting and managing in advance whether page missing such as a missing page occurs when a signature is normally stacked and bound, and a page missing testing device used for the system in a device for stacking and supplying the signature to a saddle stitching bookbinding machine.

The page missing testing device is provided with a sensor A for sensing signature supply of each feeder part and a sensor B for sensing a pusher of a gathering chain. The sensor B senses a reflection plate stuck on the pusher.