Yarn winding machine

A yarn winding machine for winding a yarn (12) on a bobbin (11) to form a yarn package (10) on the bobbin (11), comprises: a pair of bobbin holders (5, 6) having the bobbin (11) retained thereon, a pair of support arms (2, 3) swingably mounted on a stationary frame structure (1) and rotatably supporting the bobbin holders (5, 6), a friction roller (20) driven to rotate and held in frictional contact with the yarn (12) to be wound on the bobbin (11) until the yarn (12) is formed into a full yarn package (10), bobbin revolutions detecting means (40) for detecting revolutions of the bobbin (11), the revolutions detecting means (40) comprising a magnet element (41) securely fastened to a predetermined position on the peripheral portion of one of the bobbin holders (5, 6) and having a circumferential path on which the magnet element (41) revolves upon rotation of the bobbin holders (5, 6), and a detecting element (42) securely mounted on one of the support arms (2, 3), the detecting element (42) being in opposing relationship to the circumferential path of the magnet element (41) to detect the magnetic flux of the magnet element (41) and to output signals commensurate to the revolutions of the bobbin (11) for enabling determination of normal and abnormal rotational conditions of the bobbin (11).