The reading device of the present disclosure includes a housing, a first irradiation part, an imaging device, and a first diffusion part. The housing has an opening in an upper portion with a transparent reading window member. The first irradiation part emits an infrared light. The imaging device is disposed on a bottom portion such that an optical axis is directed to a reading window member. The first diffusion part is disposed on a left side wall connecting the upper and bottom portions. The first diffusion part diffuses the infrared light. The first diffusion part is made up of a light-transmitting first diffusion plate and a light-transmitting second diffusion plate. The first diffusion plate is disposed on the bottom surface side and inclined toward the upper portion. The second diffusion plate is disposed on the upper surface side and inclined toward the bottom portion.