Relay apparatus, communication system, relay method, and program

A relay apparatus comprising:

• hardware, including a processor and memory;
• a reception unit implemented at least by the hardware and configured to receive, from a private branch exchange, incoming call notification information indicating an incoming call notification indicating an incoming call to an extension representative number;
• a generation unit implemented at least by the hardware and configured to generate a push notification request corresponding to the incoming call notification for each of a plurality of mobile terminals belonging to a group of the extension representative number based on the incoming call notification information, the push notification request including a call pickup special number for responding to an incoming call to the extension representative number, the extension representative number, and a caller number of a telephone making the incoming call to the extension representative number;
• and
• a transmission unit implemented at least by the hardware and configured to perform processing for transmitting the push notification request to each mobile terminal.