PURPOSE: To achieve an accurate detection free from effect of quality of an object to be detected and environment by providing a heat generating body and a thermal detector sandwiching a delivery path of an object to be detected.

CONSTITUTION: A delivery path 1 for carrying an object 2 to be detected such as paper provided in a copying machine is made up of a guide plate 3 and a delivery roller 4. A heat generating body 5 and a thermal detector 7 are provided in a notch section 3a of a guide plate 3 sandwiching the delivery path 1. Heat rays 6 almost equal to body temperature is radiated from a heat generating surface 5a of a heat generating body 5, detected with a pyroelectric thermal detector 7 and coverted into an electrical signal which is amplified with an amplifier to drive an operation section. As the heat rays are intercepted by the object 2 being detected moving in the delivery path 1, output of the thermal detector 7 varies, leading to the detection of the object 2 being detected. The use of the heat rays eliminates effect from the variations of quality of the object, the environment and the like thereby always enabling a highly accurate detection.