To provide a detecting device for a detected body and card reader equipped therewith capable of adjusting an appropriate detecting level with simple formation even when resetting a detecting level.

The detecting device 1 for the detected body is characterized to be equipped with a light emitter 2 and a photodetector 3 to detect presence or absence of the detected body 15 by comparing the outputted level of the photodetector 3 to a predetermined detecting level and with a driving current adjusting circuit 4 adjusting the two driving current of the light emitter 2 through multistep procedures at the setup time of detecting level, while a detecting level is set based on the output level from the photodetector 3 in a condition where the light emitter 2 is forced to emit light through extinction due to driving current smaller than driving current of the ordinary use and light emitted from the light emitter 2 is not interrupted with the detected body 15.