apparatus for reciprocating a yarn guide to wind yarn on a bobbin including a rotating scroll cam provided with an endless helical cam groove and a second cam groove in superposed relationship with the endless cam groove and having a greater lead angle than the endless cam groove over a predetermined distance adjacent each turning point . the yarn guide is provided with an elongate ship - shaped cam follower slidably fitted into the endless cam groove and pivotable with respect to the yarn guide and a cylindrical cam follower slidably fitted into the second cam groove . the width of the portion of the endless cam groove adjacent each turning point is gradually increased toward the turning point so as to permit the elongate cam follower to smoothly reverse its direction when it passes the turning point .