Improving the existing limited network of observation sites and quantifying carbonyl sulfide (COS) temporal variability allows a more accurate understanding of the COS budget. A system with low-power consumption would enable COS concentration measurements at various observation sites. Therefore, we designed a continuous measurement system employing a commercially available portable laser-based analyser to measure atmospheric COS concentrations. To obtain precise atmospheric COS concentrations, (1) the temperature of the optical cell was stabilised at 0.13 ± 0.014 °C h⁻¹ using double insulation with a refrigerator and insulation material, (2) ambient air was used as a reference gas for 30 s every minute (1 cycle min⁻¹) after reducing its COS level to below 100 ppt using activated charcoal, and (3) the difference in water vapour concentration between ambient air and the reference was maintained within ± 400 ppm. The ambient COS concentrations were determined using three calibration gases with known COS concentrations prepared by the National Oceanic and Atmospheric Administration (NOAA). The analytical precision of the system was 12.1 ppt (1σ) over a 15-min, allowing for sufficient characterisation of diurnal variations of the atmospheric COS concentration. The observation in Tsukuba, Japan, showed that the observed COS concentrations in April 2023 were 410-599 ppt. Backward trajectory analysis revealed that air masses with high COS concentrations exceeding 550 ppt traversed over the Keihin Industrial Zone. This suggests that a continuous measurement system may discover potential COS sources, helping establish a COS observing network for more accurate oceanic and anthropogenic flux measurements.