The presence or absence of putting round of a yarn is detected according to whether carriers are positioned on a near side or a far side and according to the relationship of connection between loops, and the result is displayed on a monitor. On the monitor, for example, the degree of the deformation of the yarn is changed according to the presence or absence of putting round when the yarn is touched, or a color is changed according to the presence or absence of putting round. The presence or absence of putting round of the yarn can be detected and then displayed to a user.