The invention provides a communication apparatus and a communication method. The subject of the invention is that, in a spectrum sharing environment in which multiple systems communicate under the same spectrum band, the communication apparatus can reduce the depravation of receiving characteristic in its own system even if the apparatus didn't know the parameters of interference signals from other systems. In order to solve the problem, the apparatus includes a transmission pulse shaper that performs bandwidth limitation on a pulse which is used to send data symbols; a monitoring unit that monitors interference conditions from other systems different from the system to which the apparatus belongs, and availability of unused spectrum on adjacent channels of the system, a controller that controls a pulse transmission period and a pulse width of the transmission pulse shaper; and a transmission unit that transmits the band-limited signal. By monitoring the interference conditions and theavailability of unused spectrum on adjacent channels, the possessive bandwidth (i.e. pulse band) and/or the code rate (i.e. the pulse send period) of the pulse shaper are adjusted, so as to increasethe residual bandwidth of the system, restrain the interference from the other systems and increase the throughput of the system.