To directly detect bobbin unreeling tension or the like without being influenced by the variation of tension caused by other factors.

This automatic winder comprises a gate type tenser 26 applying tension to a thread unreeled from a bobbin 12 and wound on a package P, and a tension sensor 30 detecting the tension of the thread. The tension sensor 30 is arranged in a thread reeling passage Y right above the gate type tenser 26. The unreeling tension of the bobbin 12, the unreeling tension of a thread unreeling assisting device 29, and tension applied by the gate type tenser 26, can thereby be directly detected without being influenced by the variation of tension caused by the other factors. Consequently, when abnormal tension occurs, its occurrence can be immediately detected, and furthermore, the cause of the occurrence can be easily specified to prevent the occurrence of thread breakage, a package winding shape failure, or the like caused by the abnormal tension.