A communication apparatus with a directional antenna, determines, for each of receivers, transmitter antenna directivities with each of which it is possible to transmit a test signal to the receiver as a partner receiver with a main lobe; determines, as a monitor receiver, for each of the determined directivities, if the test signal is transmitted with the directivity, a receiver capable of receiving the test signal by a side lobe appended to the main lobe; decides, based on reception quality in the partner receiver by the main lobe and reception quality in the monitor receiver by the side lobe, a transmitter antenna directivity, and a partner receiver and monitor receiver as reception targets of the data out of the receivers; and transmits the data to the decided partner receiver and monitor receiver with the decided directivity.