Provided is a downlink reference signal structure suitable for increase in number of transmission layers. A radio base station device (20) has a plurality of transmission antennas; a orthogonal RS sequence generator (22) for generating orthogonal reference signals based on a two-dimensional orthogonal code, the orthogonal reference signals being orthogonalized between downlink reference signals adjacent in two-dimensional directions of frequency direction and time direction to each other in one transmission layer and being orthogonalized in different transmission layers assigned to one radio resource; a multiplexer (23) for multiplexing transmission data and the orthogonal reference signals in the one transmission layer; and a transmitter for transmitting a transmission signal obtained by multiplexing the transmission data and the orthogonal reference signals, via the transmission antenna in transmission layers simultaneously.