An endoscope system includes a processor that performs image processing on endoscope image data acquired by an endoscope, which is inserted in a subject and observes an inside of the subject. The processor communicate with a terminal device including a transceiver configured to transmit identification information identifying the terminal device, and a controller configured to: determine whether the processor is a connection destination configured to perform two-way communication, based on the received processor identification information, authenticate whether a user of the terminal device is a predetermined registered user by analyzing data obtained by the terminal device from the user, and allow two-way communication between the processor and the terminal device in response to the processor being determined as the connection designation to perform two-way communication and in response to authenticating the user of the terminal device.