A card reader may include a break-in sensing circuit and a security circuit structured to output a break-in sensing signal into the break-in sensing circuit, and receive a returned break-in sensing signal that returns from the break-in sensing circuit. The security circuit may include an output terminal to output the break-in sensing signal, and an input terminal to receive the returned break-in sensing signal. The break-in sensing signal may be input to an input section of the break-in sensing circuit, and then output from an output section of the break-in sensing circuit as the returned break-in sensing signal. The break-in sensing signal may be a pulse signal. At least either one of the output terminal and the input terminal of the security circuit may include a protection element between the terminal itself and an earth ground.