We proposed a new webcam-based air-dose rate monitoring system, in which multiple webcams are driven remotely by a single PC. A CMOS image sensor in a webcam can detect not only visible light but also ionizing radiation. Covering the lens with light shield, we can observe radiation events. Gamma-ray event rates are well used for conventional measurements of air-dose rates. The event rates in units of cpm should be converted into the air-dose rates in units of μSv/h. The conversion function was determined through measurements using a 137Cs standard gamma-ray source. To demonstrate the webcam-based monitoring system under real radiation environment, we developed monitoring software for single webcam and performed a test experiment at an irradiation room of the Kyushu University Tandem Laboratory. As a result, we confirmed that the temporal variation of the monitored air-dose rate was consistent with that of the beam current measured by a Faraday cup.