A communication medium determining apparatus determines a communication medium in use for communication between two devices on a network. The apparatus includes a communication performance obtaining unit which obtains values indicating transmission speeds in a given communication path when a device which decreases transmission speed in a specific communication medium when activated, is active and when the device is inactive. The apparatus further includes a communication medium determining unit which determines whether or not the communication through the given communication path is performed using the specific communication medium. This determination is based on a speed decrease value indicating a decrease amount of the transmission speed in the specific communication medium caused by activation of the device, and a speed difference value which is a difference in the transmission speed obtained by the communication performance obtaining unit between when the device is active and when the device is inactive.