1. A communication apparatus for decoding and displaying image data received by wireless communication, comprising: a display unit to display image data; a communication establishing unit configured to establish wireless communication with each of a computer which transmits application window data generated by executing an application program, a communication terminal which transmits video image data for video communication, and a content server which transmits content data containing a moving image; a reception unit configured to receive the application window data, the video image data, and the content data from the computer, the communication terminal, and the content server, respectively, after wireless communication has been established by the communication establishing unit; a generating unit configured to generate display image data to be displayed on the display unit by decoding the received application window data, the received video image data, and the received content data in correspondence with compression schemes of the respective data; and a control unit configured to switch decoding schemes in the generating unit in correspondence with the compression schemes of the application window data, the video image data, and the content data, wherein each of the application window data, the video image data, and the content data has been coded by using a compression scheme including orthogonal transformation processing of transforming two-dimensional image data into image data in a spatial frequency domain and quantization processing for the image data having undergone the orthogonal transformation processing, and the generating unit implements inverse orthogonal transformation processing and dequantization processing for decoding the application window data, the video image data, and the content data by a single processing circuit.