Abstract: An equalizer characteristic of an amplitude equalizer for use in a modulating and demodulating device (MODEM) can be set with considerable ease. One of a plurality of equalization characteristics assigned to an amplitude equalizer is set by generating and feeding to a transmission line a plurality of reference signals at the same level but with respectively-different frequencies. Each of such respective reference signals are received from the transmission line, separated, and measured as to its reception level. Level errors are then determined between each measured reception level and an estimated reception level previously determined in association with a respective one of the equalization characteristics. A selection and setting is then made of one of the equalization characteristics that is associated with one of the estimated receptions levels having the smallest level error.