To solve the problem that a communication state is deteriorated caused by an indoor installation place and the radio wave interference of a microwave oven or the like, a transfer rate between an intercom master unit and an intercom sub-master unit is lowered and the quality of a voice signal and an image signal is degraded due to the influence of noise in a radio communication system between the intercom master unit and an intercom sub-master unit.

The radio communication system is provided with: an image signal memory means for performing a radio communication using Bluetooth or the like between the master unit and the sub-master unit of a video intercom system, and temporarily storing the image signal in the master unit side; and an electric field strength change detection means for detecting the change of electric field strength in the radio communication between the master unit and the sub-master unit, and the sub-master unit side is provided with a sub-master unit image processing part for expanding images. On the master unit side, the image signals from an intercom slave unit are automatically stored in the image signal memory means provided on the master unit side according to the detection of the change of the electric field strength in the radio communication.