A trespass detecting system includes a motion detector installed at a specific area, detecting motion and generating a motion detect signal, and transmitting the generated motion detect signal A mobile robot photographs the specific area based on the motion detect signal and transmits the photographing image signal. A network connector transmits the motion detect signal and the image signal to a user terminal through an Internet network. A specific area of a house is monitored on a real time basis, and when a trespasser is detected in the specific area, the specific area is quickly photographed and the photographed image is transmitted to the user. Thus, an enhanced security function can be performed.