In this study, we developed a noninvasive optical transcutaneous partial pressure of carbon dioxide, pCO2, monitoring system by nondispersive infrared, NDIR. The objective of this system is to detect CO2 from the outer skin and not by an arterial blood-sampling method. There are several advantages of this system, such as short analysis time and potential for real-time monitoring. This measurement system is composed of an IR lamp, a pyroelectric sensor including a 4.26 µm optical filter, an optical gas reaction chamber, and a signal processing circuit. The pass length of the optical reaction chamber is fixed at 1 mm by soft lithography because we considered that CO2 gas is released from the human body. The fabricated pCO2 monitoring system shows a sensitivity of 6.50×10–6 absorbance/ppm in an arterial-blood CO2 concentration region of 0 to 5,000 ppm, is controlled using a mass flow controller (MFC), and has very fast response characteristics. We consider that this proposed system can be used in the optical-biosensor field for medical diagnosis, such as a pCO2 monitoring system, a capnograph system for EtCO2 analysis, and for environmental monitoring systems.