This paper presents a novel microgenerator of $CO2 (carbon dioxide) gas. NaHCO3 (sodium bicarbonate) in a chamber is decomposed by the underlaid microheater. Alternatively, water droplet is caged by paraffin layer and released by heating. The released water dissolve HOC(COOH)$(CH_2COOH)_2$ (citric acid) powder and then, NaHCO3 reacts with the solubilized HOC(COOH)$(CH_2COOH)_2$ and $CO2 is produced. Micropumps actuated by $CO2 generation were fabricated. A portable micro cell incubator of which pH is controlled by the produced $CO2 is also presented as one of the further applications.