A control device includes: a digital signal input section through which a digital signal from an external device is input through a digital signal cable; a detecting section which detects connection with the external device and then outputs a detection signal to the external device; an adjusting section which performs adjustment for the digital signal; an information input section through which display request information about a setting image which receives input of setting information about the adjustment is input; and a control section which controls the detecting section not to output the detection signal if the display request information is input.