To provide a sensor supporting device for printing medium which can maintain small transfer gaps between sensor mounting members 33, 34 without reducing the detectability of a sensor body 13 according to the open/close operation of a thermal head 20 etc. in a printing part 5, can conduct easing the loading and inserting operation of a label continuous body 7 and other printing medium and can perform easily the cleaning task for the sensor body 13 at maintenance.

According to the open/close operation of a printing part 5, the sensor mounting members 33, 34 are made capable of opening and closing. The sensor for printing medium having the sensor body 13 detecting a belt-like printing medium 7 and a couple of sensor mounting members 33, 34 faced each other is supported at the prescribed position of a transfer passage 3. A sensor open/close mechanism 31 is provided for opening and closing the sensor mounting members 33, 34 according to the open/close of the printing part 5.