An emotion detecting device includes a memory, a processor and an output/input device. An emotion template with a plurality of emotional statuses is stored in the memory. The processor is configured to receive characteristic values transformed from brain waves of a pet and determine whether the brain waves correspond to a stable state based on variation of the characteristic values during a period. When it is determined that the brain waves correspond to the stable state, the processor determines whether the brain waves match some emotional status among the emotional statuses. When the brain waves match the emotional status, the output/input device outputs information regarding the pet being in the emotional status. When the brain waves do not match any of the emotional statuses in the emotion template, the processor updates the emotion template based on a confirm operation and the characteristic values.
