It is an object of the present invention to provide a communication device, a digital signature verification method, and a digital signature generation method, in which the memory usage efficiency is improved without confidential information required for the verification or generation of a signature being easily leaked to the outside.The Java application judges whether signature verification is required for the received signature target data. When judging that signature verification is required, the Java application outputs the received signature target data to the PKI of the platform. The PKI verifies the signature that has been added to the data output by the Java application and performs signature generation, and then notifies the Java application.