To provide a communication system for spontaneously starting a specific communication event by a user operation at a peripheral equipment side although the issue direction of a command in charge of the execution of a communication event is controlled to one direction from a PC side to the peripheral equipment side.

A peripheral equipment side trigger for requesting a host device to start an object communication event is generated based on a user operation, and a host device side issues a trigger report request command for monitoring the generation of the peripheral equipment side trigger in peripheral equipment configured as an image processor to the peripheral equipment according to a main communication protocol. Trigger generation report information from the peripheral equipment which has received this is received by the host equipment side, and when it is decided that the peripheral equipment side trigger is present from the content of the trigger generation report information, the object communication event is started.

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