This invention provides a zero gas refiner for CO2 concentration measurement device that can continuously refine a zero gas that is preferable for CO2 concentration measurement. This invention adopts the zero gas refiner comprising a water adsorbent and a CO2 adsorbent that desorb an adsorbed component and restore an adsorption ability by being heated to a predetermined restoration temperature, a refiner body that adsorbs water and CO2 in an introduced sample gas or air in this order by the use of the water adsorbent and the CO2 adsorbent housed inside of the refiner body so as to refine a zero gas and that leads out the zero gas, and a heating mechanism that applies heat to the refiner body at a time when the adsorption ability of the water adsorbent or the CO2 adsorbent drops to an amount that is less than or equal to a predetermined amount.