The present invention relates to a front-end event detector for detecting the occurrence of an event before a signal process is generated, and a low power camera system maintaining the low-power mode when idle but activated in normal mode only when the occurrence of an event is detected in the front-end event detector. The front-end event detector according to the present invention comprises: an image sensor for obtaining analog image data and converting them into digital image data; a first buffer memory for storing the digital image data; a first comparator, wherein the next digital image data delivered from the image sensor is compared to the digital image data stored in the first buffer memory for generating activation signals when the occurrence of an event is detected and transmitting them to an external device; an image signal processor for image data processing the digital image delivered from the first comparator.