1. A security system comprising: a first sensor disposed in an area to be monitored in a building, to monitor the area; a moving robot having a robot main body, a second sensor for monitoring the area to be monitored and a robot operation processor for moving the robot main body according to an operation mode data indicating an operation of the robot main body; and a controller including first and second sensor information monitor means for collecting first sensor information and second sensor information which are acquired by the first and second sensors, and an operation mode data generator for generating the operation mode data from the first sensor information or the second sensor information and transmitting the operation mode data to the robot operation processor, wherein the controller further includes a remark level data memory storing remark level data indicating a monitoring weight for a target to be monitored by the first sensor or the second sensor, the remark level data processor renews the remark level data in the remark level data memory by using the first or the second sensor information during a patrol operation of the robot, and the moving robot patrols in the building on the basis on the remark level data and the operation mode data.