This report describes the technical characteristics and measurement results of a real time PCB gas monitoring system (MOHMS-21GP) developed by Mitsubishi Heavy Industries, Ltd. (MHI). The characteristics of the gas direct introduction type laser ionization TOFMS (Time of Flight Mass Spectrometry), which indicates the measuring principle of this device, are described. A detecting sensitivity of 0.01 mg/m³N, equivalent to 1/15 of the limit specified by regulatory requirements, was achieved. The measurement test results obtained using the exhaust gas from a PCB disposal plant (MHI) are also presented.