A communication device, a communication system and an authentication system for preventing a disguising act by an illegal man-in-the-middle and improving the safety and certainty of authentication processing are provided. A slave (20) transmits an authentication request including device information to a master (10). The master (10) receives the authentication request and displays the device information included in the authentication request on a screen of a display section (13). The user visually checks the device information displayed on the screen of the display section 13 (13), determines whether or not to verify the authentication, and instructs the master (10) of the determination result via an input section (14). The master (10), instructed to verify or not to verify the authentication, transmits a response in accordance with the instruction to the slave (20).