Textile-material monitoring device and yarn winding apparatus

A textile-material monitoring device (11) that can improve accuracy in detection of a foreign matter by reducing shadows during the detection and detect a thickness irregularity of a textile material (10) favorably is provided. A clearer of the textile-material monitoring includes a light source unit (36), a light receiving unit (37) that doubles as a transmitted-light receiving unit and a reflected-light receiving unit, and a diffuser member (38). The light receiving unit (37) receives, of light emitted from the light source unit (36) toward a running spun yarn, light transmitted through the spun yarn and light reflected from the same. The diffuser member (38) arranged between the light source unit. (36) and the spun yarn (10) diffuses the light emitted from the light source unit (36) such that a degree of light diffusion in a plane orthogonal to a running direction of the spun yarn is greater than a degree of light diffusion in a plane parallel to the running direction.