With 15 wt.%WO3/TiO2 as the basic sensor substance, various metal catalysts were added. As shown in Fig. 8, the sensor material added with 1 wt.%In is better in sensitivity than other metal catalysts. This means that 1 wt.%In/15 wt.%WO3/TiO2 sensor substance oxidizes the mixed gas with trimethylamine and ammonia than other sensor substances, and shows better selectivity.