A printer having a digital camera connected thereto checks whether or not a transfer button of the camera is pressed, and checks the communication mode of the camera in the case where it is pressed. In the case where the communication mode of the camera is a mass storage mode, a conversion command for ordering change to a PTP mode is sent to the camera from the printer. The camera performs a bus reset so as to redo configuration and convert the protocol to the PTP mode. In the case where the communication mode of the camera is the PTP mode or is automatically changed to the PTP mode, the image is transferred to the printer in conjunction with operation of the transfer button. Thus, a desired image is transferred to a host such as the printer according to a transfer instruction of an image by the transfer button, etc. on a device side while a user is not conscious of the state of a communication mode and mode switching of the device such as the digital camera.