A host computer can prevent a peripheral device connected to the host computer from unexpectedly shifting into a non-connection state through control of the host computer. Further, when the peripheral device, such as an electronic camera, cannot receive enough power from a connection line, such as a USB, the peripheral is still able to use the available power effectively. To achieve these objectives, there is a disclosed computer peripheral device connected to the host computer, wherein the peripheral device is comprised of a connection signal transmitter and a controller. The connection signal transmitter is used to transmit from the peripheral device to the host computer a signal to control the connection with the host computer. The controller is used for proceeding a running state of the computer peripheral to a non-connection state, after the connection signal transmitter transmits a signal for a non-connection state to the host computer.