PURPOSE: To obtain the 3-position of knit, tuck and welt by relatively simple combination and handling and the 4-position preferably by adjusting a supporting position.

CONSTITUTION: This cam device is equipped with at least two kinds of knitting needles 1 and 2 having master butts 1A and 2A and at least two selecting butts 1C, 1E, 2C and 2E, a stitch cam 5 for lowering the master butts to a stitch forming level and a needle selecting means which controls the selecting butts and is capable of choosing three positions of knit, tuck and welt. The cam device is further provided with a knitting cam 7 which chooses the selecting butt to lower it to a stitch forming level, engages/disengages it and is longitudinally movably arranged, a tuck cam 6 which chooses the selecting butt to lower it to a stitch forming level, engages/disengages it and is longitudinally movably arranged, a welt guard cam 8 for controlling advance of the knitting needle at the welt position and a needle selecting means 11 for individually choosing these cams.