Provided are a sinker that is unlikely to cause the positions of a plating yarn and a ground yarn to be reversed unintentionally, and a knitting mechanism using the sinker. In a knitting mechanism with which plating knitting can be performed on a circular knitting machine, a sinker has a first transition surface (42, 42B) and a second transition surface (43, 43B) on a sinker top thereof. Either a first route (61, 61A) or a second route (62, 62A) is selected as a movement route for the sinker. The first route (61, 61A) brings the first transition surface (42, 42B) into the closest proximity to a knitting needle when the knitting needle is being lowered, and allows the knitting needle to be lowered in this state to the lowest point of a movement route of the knitting needle. The second route (62, 62A) brings the second transition surface (43, 43B) into the closest proximity to the knitting needle when the knitting needle is being lowered, and allows the knitting needle to be lowered in this state to the lowest point of the movement route of the knitting needle. Thus, during plating knitting on the circular knitting machine, knitting can be performed by interchanging positions of a first yarn (71, 71A) and a second yarn (72, 72A).