Abstract: Provided is a communication medium determining apparatus which easily determines a communication medium in use for communication between two devices on a network, including: a communication performance obtaining unit (303) 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; and a communication medium determining unit (301) which determines whether or not the communication through the given communication path is performed using the specific communication medium, based on (i) a speed decrease value indicating an amount of decrease in the transmission speed in the specific communication medium caused by activation of the device and (ii) a speed difference value which is a difference in the transmission speed obtained by the communication performance obtaining unit (303) between when the device is active and when the device is inactive.