PURPOSE: To provide a yarn feeder which executes yarn feeding by a yarn reserve support spool.

CONSTITUTION: The support spool is so arranged as to be rotated by a motor 60. The yarn is taken up and unwound from the spool as the spool rotates. The rewinding of the yarn reserve on the spool is not controlled. The size of the yarn reserve is monitored and the yarn taking-up is controlled according thereto. The unit 3 includes electrically contactless detection and control elements 3 as well. These elements are placed immediately adjacently to the rotary spool. The unit 3 is so designed as to detect the presence and quantity of the yarn on the yarn reserve support surface 10. The unit also controls the motor 60 described above.