A security system comprises 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; a controller including first and second sensor information monitor units 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.