A data relay apparatus includes a first demodulating unit, demodulating a modulation signal of a first modulation mode from a first transmission source; a second demodulating unit, demodulating a modulation signal from a second transmission source, having a modulation mode higher than the first modulation mode; a combination controlling unit, providing a mapping rule necessary for performing signal combination in accordance with the modulation mode of the modulation signal from each of the first and second transmission source, the mapping rule to map the demodulated modulation signal from the first transmission source together with the demodulated modulation signal from the second transmission source to a constellation of symbols of the second modulation mode; a data combining unit, performing data combination on the demodulated modulation signal from the first transmission source and the demodulated modulation signal from the second transmission source according to the mapping rule.