A coupling device 20 includes a first resistive element 22, and a single-pole single-throw switch 21 that is controlled by a digital camera 10 to, in a coupled state in which the digital camera 10 is coupled to an accessory 30, switch an electrical connection state of the first resistive element 22 and a second resistive element 31 included in the accessory 30 to a resistance detection terminal D2 of the digital camera 10 between a first connection state in which the second resistive element 31 is connected to the resistance detection terminal D2 and a second connection state in which the first resistive element 22 and the second resistive element 31 are connected to the resistance detection terminal D2.