PURPOSE: To provide sensor mounting members capable of easy positioning with simple structure.

CONSTITUTION: A conveyer roller 4 is fitted between frames 2 and 2 opposing to each other by bearings 42 and 42, and a conveyer belt 15 is belted. The placing surface 63 of sensor mounting members 17 and 18, in a sensor member containing section 52 of which a reflection plate 50 and photosensor 51 are contained, is placed on the top of a frame 2, and the mounting face 64, which is perpendicular to this placing surface 63 and is extended from the placing surface 63, is mounted on the side face of the frame 2. A hole section 67 and the first mounting groove 21 are fastened with a bolt 81 and nut 82 threadedly fitted.