A communication apparatus including: a despreading section despreading a reception signal with a spreading code defined in one communication system; a decoding section decoding the reception signal despread by the despreading section; and a first occupation detection section correlatively detecting an occupation state of a communication band with a preamble code defined in the communication system; and a second occupation detection section correlatively detecting an occupation state of a communication band of a signal of another communication system, the signal being expected to arrive as an interference wave, with a preamble code defined in the another communication system.