The present invention obtains a processing device and processing method, a warning system, and a saddle-type vehicle capable of achieving both improvement in rider safety and improvement in comfort. The processing device (20) is to the acquisition unit that acquires the surrounding environment information according to the output of the surrounding environment detection device (11) while the saddle-mounted vehicle (100) is traveling, and to the rider that is generated in the warning system (1). It is provided with a determination unit for determining the necessity of the warning operation and a control unit for causing the notification device (30) to execute the warning operation when the determination unit determines that the warning operation is necessary. Further, while the saddle-mounted vehicle (100) is running, the helmet attitude direction information according to the output of the helmet attitude direction detection device (13) is acquired, and the determination unit is based on the surrounding environment information and the helmet attitude direction information. Then, the necessity of the warning operation is determined.
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