The instant disclosure provides a non-contact temperature measuring device including a base, a temperature measuring module, a light module and a reflecting module. The temperature measuring module is disposed on the base. The temperature measuring module has a measuring area. The light module is disposed on the base and is configured to generate a projecting light. The reflecting module is disposed on the base and has a reflecting surface. The projecting light is projected onto the reflecting surface and is reflected by the reflecting surface, thereby forming at least two reflecting light beams adjacent to the measuring area. The at least two reflecting light beams surround a marking area which is able to overlap with the measuring area, and the range of the marking area changes according to the distance between the object to be measured and the non-contact temperature measuring device.