[Object] To enhance accuracy at the time of setting with consideration of a cell size of a code when an exposure time is automatically set. [Means to solve the problems] An upper limit of an exposure time of an imaging part as a restriction condition for reading a code attached to a workpiece is calculated based on a moving speed of the workpiece, which is inputted by an input part, and a cell size, which is calculated by a cell size calculation part. An exposure time of the imaging part is set within the restriction condition by analyzing a plurality of images, which includes a code and is obtained by taking images multiple times by changing the exposure time of the imaging part.