A communications apparatus which ensures a predetermined communication quality even when an external environment changes dynamically, and enhances a throughput for overall system, thereby achieving favorable transmission efficiency. A communications apparatus having a receiver and a transmitter and carries out sending/receiving by use of a pulse train is provided with a communication environment measuring section to measure a communication status based on an output from the receiver. The transmitter is configured such that it transmits a transmission signal, in which the transmission rate of data to be transmitted and the pulse energy have been controlled in association with each other, according to a result of the measurement.