Monitor camera units, a data storing unit, a control server, and a monitor display are coupled by a network. The monitor camera unit includes a motion detector for detecting motion from video data, a microphone, a traffic monitor, a memory for storing the video data, and a sensor signal input circuit. The traffic monitor monitors the traffic of the network. If the traffic is high, only necessary data or sound data is transmitted. The memory stores the video data in response to the motion detector and a thinning circuit thins the video data from the memory in response to a sensor signal. The control server receives the alarm data from the monitor camera and further receives the alarm type data, time data, position data of a pivoting unit for pivoting the camera unit and transmits the data to the display terminal. In the presence of a loud sound, alarm data is also generated but it is not sent if a switch is OFF. The control server includes a data base storing set of alarm data. If an operator judges one set of alarm data is an error, the set of data is not erased but mark data is correspondingly stored to inhibit searching the set of data. During the night, the exposure and transmitting intervals are increased to prevent the same data from being transmitted twice.